EVF Eaton Vance Senior Income

Semiannual Report December 31, 2022

Eaton Vance

Senior Income Trust

Table of Contents
Performance	2
Fund Profile	3
Endnotes and Additional Disclosures	4
Financial Statements	5
Annual Meeting of Shareholders	34
Officers and Trustees	35
Privacy Notice	36
Important Notices	38

Eaton Vance

Senior Income Trust

December 31, 2022

Performance

Portfolio Manager(s) John Redding, Andrew N. Sveen, CFA, Catherine C. McDermott, Daniel P. McElaney, CFA and Sarah A. Choi

% Average Annual Total Returns1,2	Inception Date	Six Months	One Year	Five Years	Ten Years
Fund at NAV	10/30/1998	2.57%	(7.06)%	2.90%	4.34%
Fund at Market Price	—	1.86	(14.74)	2.46	2.89
Morningstar® LSTA® US Leveraged Loan IndexSM	—	4.14%	(0.60)%	3.31%	3.67%

% Premium/Discount to NAV3
As of period end	(10.53)%

See Endnotes and Additional Disclosures in this report.

Past performance is no guarantee of future results. Returns are historical and are calculated net of management fees and other expenses by determining the percentage change in net asset value (NAV) or market price (as applicable) with all distributions reinvested in accordance with the Fund’s Dividend Reinvestment Plan. Furthermore, returns do not reflect the deduction of taxes that shareholders may have to pay on Fund distributions or upon the sale of Fund shares. Performance at market price will differ from performance at NAV due to variations in the Fund’s market price versus NAV, which may reflect factors such as fluctuations in supply and demand for Fund shares, changes in Fund distributions, shifting market expectations for the Fund’s future returns and distribution rates, and other considerations affecting the trading prices of closed-end funds. Investment return and principal value will fluctuate so that shares, when sold, may be worth more or less than their original cost. Performance for periods less than or equal to one year is cumulative. Performance is for the stated time period only; due to market volatility, current Fund performance may be lower or higher than the quoted return. For performance as of the most recent month-end, please refer to eatonvance.com.

2

Eaton Vance

Senior Income Trust

December 31, 2022

Endnotes and Additional Disclosures

4

Eaton Vance

Senior Income Trust

December 31, 2022

Portfolio of Investments (Unaudited) — continued

Convertible Preferred Stocks — 0.0%(6)

Security	Shares		Value
Electronics/Electrical — 0.0%(6)
Riverbed Technology, Inc., Series A, 6.50%, (1.50% cash, 5.00% PIK)(5)		28	$          21
			$         21
Oil and Gas — 0.0%
Nine Point Energy Holdings, Inc., Series A, 12.00%, (PIK)(3)(4)(7)		5	$           0
			$          0
Total Convertible Preferred Stocks (identified cost $5,829)			$         21

Corporate Bonds — 7.0%

Security	Principal Amount (000's omitted)		Value
Aerospace and Defense — 0.1%
TransDigm, Inc., 4.875%, 5/1/29	$	135	$     117,926
			$    117,926
Automotive — 0.5%
Clarios Global, L.P./Clarios U.S. Finance Co., 8.50%, 5/15/27(1)	$	500	$     489,278
			$    489,278

Eaton Vance

Senior Income Trust

December 31, 2022

Portfolio of Investments (Unaudited) — continued

Senior Floating-Rate Loans — 128.6%(9)

Borrower/Description	Principal Amount* (000's omitted)		Value
Aerospace and Defense — 2.0%
Aernnova Aerospace S.A.U.:
Term Loan, 5.436%, (6 mo. EURIBOR + 3.00%), 2/26/27	EUR	696	$     674,049
Term Loan, 5.625%, (6 mo. EURIBOR + 3.00%), 2/26/27	EUR	179	172,833
IAP Worldwide Services, Inc., Term Loan - Second Lien, 11.23%, (3 mo. USD LIBOR + 6.50%), 7/18/23(3)		203	158,475
WP CPP Holdings, LLC, Term Loan, 8.17%, (3 mo. USD LIBOR + 3.75%), 4/30/25		1,167	1,022,695
			$  2,028,052

Eaton Vance

Senior Income Trust

December 31, 2022

Portfolio of Investments (Unaudited) — continued

Eaton Vance

Senior Income Trust

December 31, 2022

Portfolio of Investments (Unaudited) — continued

Eaton Vance

Senior Income Trust

December 31, 2022

Portfolio of Investments (Unaudited) — continued

Eaton Vance

Senior Income Trust

December 31, 2022

Portfolio of Investments (Unaudited) — continued

Eaton Vance

Senior Income Trust

December 31, 2022

Portfolio of Investments (Unaudited) — continued

Eaton Vance

Senior Income Trust

December 31, 2022

Portfolio of Investments (Unaudited) — continued

Eaton Vance

Senior Income Trust

December 31, 2022

Portfolio of Investments (Unaudited) — continued

Eaton Vance

Senior Income Trust

December 31, 2022

Portfolio of Investments (Unaudited) — continued

Eaton Vance

Senior Income Trust

December 31, 2022

Portfolio of Investments (Unaudited) — continued

Warrants — 0.0%

Security	Shares		Value
Leisure Goods/Activities/Movies — 0.0%
Cineworld Group PLC, Exp. 11/23/25(4)(5)		102,872	$           0
			$          0
Retailers (Except Food and Drug) — 0.0%
David’s Bridal, LLC, Exp. 12/31/28(3)(4)(5)		2,169	$           0
			$          0
Total Warrants (identified cost $0)			$          0

Miscellaneous — 0.0%

Security	Shares		Value
Cable and Satellite Television — 0.0%
ACC Claims Holdings, LLC(3)(4)		200,340	$           0
Total Miscellaneous (identified cost $0)			$          0

Short-Term Investments — 3.0%

Security	Shares		Value
Morgan Stanley Institutional Liquidity Funds - Government Portfolio, Institutional Class, 4.11%(14)		3,052,641	$   3,052,641
Total Short-Term Investments (identified cost $3,052,641)			$  3,052,641
Total Investments — 153.5% (identified cost $175,054,211)			$158,715,809
Less Unfunded Loan Commitments — (0.0)%(6)			$     (49,945)
Net Investments — 153.5% (identified cost $175,004,266)			$158,665,864
Other Assets, Less Liabilities — (17.1)%			$ (17,646,433)
Auction Preferred Shares Plus Cumulative Unpaid Dividends — (36.4)%			$ (37,617,347)
Net Assets Applicable to Common Shares — 100.0%			$103,402,084

Eaton Vance

Senior Income Trust

December 31, 2022

Portfolio of Investments (Unaudited) — continued

17

See Notes to Financial Statements.

Eaton Vance

Senior Income Trust

December 31, 2022

Portfolio of Investments (Unaudited) — continued

18

See Notes to Financial Statements.

Eaton Vance

Senior Income Trust

December 31, 2022

Statement of Assets and Liabilities (Unaudited)

	December 31, 2022
Assets
Unaffiliated investments, at value (identified cost $171,951,625)	$ 155,613,223
Affiliated investment, at value (identified cost $3,052,641)	3,052,641
Cash	2,065,164
Deposits for derivatives collateral — forward foreign currency exchange contracts	630,000
Foreign currency, at value (identified cost $635,007)	644,899
Interest and dividends receivable	1,273,818
Dividends receivable from affiliated investment	7,952
Receivable for investments sold	1,578,776
Prepaid upfront fees on notes payable	13,200
Prepaid expenses	31,116
Total assets	$164,910,789
Liabilities
Notes payable	$ 18,000,000
Payable for investments purchased	4,164,481
Payable for open forward foreign currency exchange contracts	420,497
Distributions payable	876,943
Payable to affiliates:
Investment adviser fee	95,791
Administration fee	33,377
Trustees' fees	3,190
Accrued expenses	297,079
Total liabilities	$ 23,891,358
Auction preferred shares (1,504 shares outstanding) at liquidation value plus cumulative unpaid dividends	$ 37,617,347
Net assets applicable to common shares	$103,402,084
Sources of Net Assets
Common shares, $0.01 par value, unlimited number of shares authorized	$ 175,389
Additional paid-in capital	139,381,950
Accumulated loss	(36,155,255)
Net assets applicable to common shares	$103,402,084
Common Shares Issued and Outstanding	17,538,858
Net Asset Value Per Common Share
Net assets ÷ common shares issued and outstanding	$ 5.90

19

See Notes to Financial Statements.

Eaton Vance

Senior Income Trust

December 31, 2022

Statement of Operations (Unaudited)

	Six Months Ended
	December 31, 2022
Investment Income
Dividend income	$ 228,409
Dividend income from affiliated investment	32,850
Interest income	6,576,316
Total investment income	$ 6,837,575
Expenses
Investment adviser fee	$ 592,962
Administration fee	205,890
Trustees’ fees and expenses	7,167
Custodian fee	42,601
Transfer and dividend disbursing agent fees	10,042
Legal and accounting services	140,818
Printing and postage	67,279
Interest expense and fees	453,947
Preferred shares service fee	16,304
Miscellaneous	32,588
Total expenses	$ 1,569,598
Deduct:
Waiver and/or reimbursement of expenses by affiliate	$ 1,858
Total expense reductions	$ 1,858
Net expenses	$ 1,567,740
Net investment income	$ 5,269,835
Realized and Unrealized Gain (Loss)
Net realized gain (loss):
Investment transactions	$ (3,115,798)
Foreign currency transactions	18,245
Forward foreign currency exchange contracts	459,478
Net realized loss	$(2,638,075)
Change in unrealized appreciation (depreciation):
Investments	$ 974,121
Foreign currency	6,832
Forward foreign currency exchange contracts	(541,657)
Net change in unrealized appreciation (depreciation)	$ 439,296
Net realized and unrealized loss	$(2,198,779)
Distributions to preferred shareholders	$ (685,089)
Net increase in net assets from operations	$ 2,385,967

20

See Notes to Financial Statements.

Eaton Vance

Senior Income Trust

December 31, 2022

Statements of Changes in Net Assets

	Six Months Ended December 31, 2022 (Unaudited)	Year Ended June 30, 2022
Increase (Decrease) in Net Assets
From operations:
Net investment income	$ 5,269,835	$ 6,978,641
Net realized gain (loss)	(2,638,075)	4,702,186
Net change in unrealized appreciation (depreciation)	439,296	(21,205,612)
Distributions to preferred shareholders	(685,089)	(113,201)
Net increase (decrease) in net assets from operations	$ 2,385,967	$ (9,637,986)
Distributions to common shareholders	$ (5,191,502)	$ (7,219,500)
Tax return of capital to common shareholders	$ —	$ (341,150)
Capital share transactions:
Reinvestment of distributions to common shareholders	$ —	$ 17,633
Cost of shares repurchased in tender offer (see Note 6)	—	(138,036,580)
Net decrease in net assets from capital share transactions	$ —	$(138,018,947)
Net decrease in net assets	$ (2,805,535)	$(155,217,583)
Net Assets Applicable to Common Shares
At beginning of period	$ 106,207,619	$ 261,425,202
At end of period	$103,402,084	$ 106,207,619

21

See Notes to Financial Statements.

Eaton Vance

Senior Income Trust

December 31, 2022

Statement of Cash Flows (Unaudited)

	Six Months Ended
	December 31, 2022
Cash Flows From Operating Activities
Net increase in net assets from operations	$ 2,385,967
Distributions to preferred shareholders	685,089
Net increase in net assets from operations excluding distributions to preferred shareholders	$ 3,071,056
Adjustments to reconcile net increase in net assets from operations to net cash provided by operating activities:
Investments purchased	(21,181,940)
Investments sold and principal repayments	30,172,797
Increase in short-term investments, net	(553,049)
Net amortization/accretion of premium (discount)	(291,994)
Amortization of prepaid upfront fees on notes payable	37,904
Increase in interest and dividends receivable	(329,237)
Increase in dividends receivable from affiliated investment	(6,983)
Decrease in receivable for open forward foreign currency exchange contracts	177,623
Increase in prepaid expenses	(26,758)
Increase in payable for open forward foreign currency exchange contracts	364,034
Decrease in payable to affiliate for investment adviser fee	(5,153)
Decrease in payable to affiliate for administration fee	(1,706)
Increase in payable to affiliate for Trustees' fees	787
Increase in accrued expenses	56,110
Decrease in unfunded loan commitments	(265,249)
Net change in unrealized (appreciation) depreciation from investments	(974,121)
Net realized loss from investments	3,115,798
Net cash provided by operating activities	$ 13,359,919
Cash Flows From Financing Activities
Cash distributions paid to common shareholders	$ (4,314,559)
Cash distributions paid to preferred shareholders	(677,032)
Proceeds from notes payable	9,000,000
Repayments of notes payable	(17,000,000)
Net cash used in financing activities	$(12,991,591)
Net increase in cash and restricted cash*	$ 368,328
Cash at beginning of period (including foreign currency)	$ 2,971,735
Cash and restricted cash at end of period (including foreign currency)	$ 3,340,063
Supplemental disclosure of cash flow information:
Cash paid for interest and fees on borrowings	$ 392,863

*	Includes net change in unrealized appreciation (depreciation) on foreign currency of $7,464.

The following table provides a reconciliation of cash and restricted cash reported within the Statement of Assets and Liabilities that sum to the total of such amounts shown on the Statement of Cash Flows.

22

See Notes to Financial Statements.

23

See Notes to Financial Statements.

Eaton Vance

Senior Income Trust

December 31, 2022

Notes to Financial Statements (Unaudited)

1  Significant Accounting Policies

Eaton Vance Senior Income Trust (the Trust) is a Massachusetts business trust registered under the Investment Company Act of 1940, as amended (the 1940 Act), as a diversified, closed-end management investment company. The Trust’s investment objective is to provide a high level of current income, consistent with the preservation of capital, by investing primarily in senior, secured floating-rate loans.

The following is a summary of significant accounting policies of the Trust. The policies are in conformity with accounting principles generally accepted in the United States of America (U.S. GAAP). The Trust is an investment company and follows accounting and reporting guidance in the Financial Accounting Standards Board (FASB) Accounting Standards Codification Topic 946.

A  Investment Valuation—The following methodologies are used to determine the market value or fair value of investments.

Senior Floating-Rate Loans. Interests in senior floating-rate loans (Senior Loans) are valued generally at the average mean of bid and ask quotations obtained from a third party pricing service. Senior Loans, for which a valuation is not available or deemed unreliable, are fair valued by the investment adviser utilizing one or more of the valuation techniques described below to assess the likelihood that the borrower will make a full repayment of the loan underlying such Senior Loan. If the investment adviser believes that there is a reasonable likelihood of full repayment, the investment adviser will determine fair value using a matrix pricing approach that considers the yield on the Senior Loan relative to yields on other Senior Loans issued by companies of comparable credit quality. If the investment adviser believes there is not a reasonable likelihood of full repayment, the investment adviser will determine fair value using analyses that include, but are not limited to: (i) a comparison of the value of the borrower’s outstanding equity and debt to that of comparable public companies; (ii) a discounted cash flow analysis; or (iii) when the investment adviser believes it is likely that a borrower will be liquidated or sold, an analysis of the terms of such liquidation or sale. In certain cases, the investment adviser will use a combination of analytical methods to determine fair value, such as when only a portion of a borrower’s assets are likely to be sold. In conducting its assessment and analyses for purposes of determining fair value of a Senior Loan, the investment adviser will use its discretion and judgment in considering and appraising relevant factors. Junior Loans (i.e., subordinated loans and second lien loans) are valued in the same manner as Senior Loans.

Debt Obligations. Debt obligations are generally valued on the basis of valuations provided by third party pricing services, as derived from such services’ pricing models. Inputs to the models may include, but are not limited to, reported trades, executable bid and ask prices, broker/dealer quotations, prices or yields of securities with similar characteristics, interest rates, anticipated prepayments, benchmark curves or information pertaining to the issuer, as well as industry and economic events. The pricing services may use a matrix approach, which considers information regarding securities with similar characteristics to determine the valuation for a security. Short-term debt obligations purchased with a remaining maturity of sixty days or less for which a valuation from a third party pricing service is not readily available may be valued at amortized cost, which approximates fair value.

Equity Securities. Equity securities listed on a U.S. securities exchange generally are valued at the last sale or closing price on the day of valuation or, if no sales took place on such date, at the mean between the closing bid and ask prices on the exchange where such securities are principally traded. Equity securities listed on the NASDAQ National Market System are valued at the NASDAQ official closing price. Unlisted or listed securities for which closing sales prices or closing quotations are not available are valued at the mean between the latest available bid and ask prices or, in the case of preferred equity securities that are not listed or traded in the over-the-counter market, by a third party pricing service that uses various techniques that consider factors including, but not limited to, prices or yields of securities with similar characteristics, benchmark yields, broker/dealer quotes, quotes of underlying common stock, issuer spreads, as well as industry and economic events.

Derivatives. Forward foreign currency exchange contracts are generally valued at the mean of the average bid and average ask prices that are reported by currency dealers to a third party pricing service at the valuation time. Such third party pricing service valuations are supplied for specific settlement periods and the Trust’s forward foreign currency exchange contracts are valued at an interpolated rate between the closest preceding and subsequent settlement period reported by the third party pricing service.

Foreign Securities and Currencies. Foreign securities and currencies are valued in U.S. dollars, based on foreign currency exchange rate quotations supplied by a third party pricing service. The pricing service uses a proprietary model to determine the exchange rate. Inputs to the model include reported trades and implied bid/ask spreads.

Other. Investments in management investment companies (including money market funds) that do not trade on an exchange are valued at the net asset value as of the close of each business day.

Fair Valuation. In connection with Rule 2a-5 of the 1940 Act, which became effective September 8, 2022, the Trustees have designated the Trust’s investment adviser as its valuation designee. Investments for which valuations or market quotations are not readily available or are deemed unreliable are valued by the investment adviser, as valuation designee, at fair value using methods that most fairly reflect the security’s “fair value”, which is the amount that the Trust might reasonably expect to receive for the security upon its current sale in the ordinary course. Each such determination is based on a consideration of relevant factors, which are likely to vary from one pricing context to another. These factors may include, but are not limited to, the type of security, the existence of any contractual restrictions on the security’s disposition, the price and extent of public trading in similar securities of the issuer or of comparable companies or entities, quotations or relevant information obtained from broker/dealers or other market participants, information obtained from the issuer, analysts, and/or the appropriate stock exchange (for exchange-traded securities), an analysis of the company’s or entity’s financial statements, and an evaluation of the forces that influence the issuer and the market(s) in which the security is purchased and sold.

25

Eaton Vance

Senior Income Trust

December 31, 2022

Notes to Financial Statements (Unaudited) — continued

B  Investment Transactions—Investment transactions for financial statement purposes are accounted for on a trade date basis. Realized gains and losses on investments sold are determined on the basis of identified cost.

C  Income—Interest income is recorded on the basis of interest accrued, adjusted for amortization of premium or accretion of discount. Fees associated with loan amendments are recognized immediately. Dividend income is recorded on the ex-dividend date for dividends received in cash and/or securities. Distributions from investment companies are recorded as dividend income, capital gains or return of capital based on the nature of the distribution.

D  Federal Taxes—The Trust's policy is to comply with the provisions of the Internal Revenue Code applicable to regulated investment companies and to distribute to shareholders each year substantially all of its net investment income, and all or substantially all of its net realized capital gains. Accordingly, no provision for federal income or excise tax is necessary.

As of December 31, 2022, the Trust had no uncertain tax positions that would require financial statement recognition, de-recognition, or disclosure. The Trust files a U.S. federal income tax return annually after its fiscal year-end, which is subject to examination by the Internal Revenue Service for a period of three years from the date of filing.

E  Foreign Currency Translation—Investment valuations, other assets, and liabilities initially expressed in foreign currencies are translated each business day into U.S. dollars based upon current exchange rates. Purchases and sales of foreign investment securities and income and expenses denominated in foreign currencies are translated into U.S. dollars based upon currency exchange rates in effect on the respective dates of such transactions. Recognized gains or losses on investment transactions attributable to changes in foreign currency exchange rates are recorded for financial statement purposes as net realized gains and losses on investments. That portion of unrealized gains and losses on investments that results from fluctuations in foreign currency exchange rates is not separately disclosed.

F  Unfunded Loan Commitments—The Trust may enter into certain loan agreements all or a portion of which may be unfunded. The Trust is obligated to fund these commitments at the borrower's discretion. These commitments are disclosed in the accompanying Portfolio of Investments. At December 31, 2022, the Trust had sufficient cash and/or securities to cover these commitments.

G  Use of Estimates—The preparation of the financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities at the date of the financial statements and the reported amounts of income and expense during the reporting period. Actual results could differ from those estimates.

H  Indemnifications—Under the Trust’s organizational documents, its officers and Trustees may be indemnified against certain liabilities and expenses arising out of the performance of their duties to the Trust. Under Massachusetts law, if certain conditions prevail, shareholders of a Massachusetts business trust (such as the Trust) could be deemed to have personal liability for the obligations of the Trust. However, the Trust’s Declaration of Trust contains an express disclaimer of liability on the part of Trust shareholders and the By-laws provide that the Trust shall assume, upon request by the shareholder, the defense on behalf of any Trust shareholders. Moreover, the By-laws also provide for indemnification out of Trust property of any shareholder held personally liable solely by reason of being or having been a shareholder for all loss or expense arising from such liability. Additionally, in the normal course of business, the Trust enters into agreements with service providers that may contain indemnification clauses. The Trust's maximum exposure under these arrangements is unknown as this would involve future claims that may be made against the Trust that have not yet occurred.

I  Forward Foreign Currency Exchange Contracts—The Trust may enter into forward foreign currency exchange contracts for the purchase or sale of a specific foreign currency at a fixed price on a future date. The forward foreign currency exchange contracts are adjusted by the daily exchange rate of the underlying currency and any gains or losses are recorded as unrealized until such time as the contracts have been closed. Risks may arise upon entering these contracts from the potential inability of counterparties to meet the terms of their contracts and from movements in the value of a foreign currency relative to the U.S. dollar.

J  Interim Financial Statements—The interim financial statements relating to December 31, 2022 and for the six months then ended have not been audited by an independent registered public accounting firm, but in the opinion of the Trust’s management, reflect all adjustments, consisting only of normal recurring adjustments, necessary for the fair presentation of the financial statements.

2  Auction Preferred Shares

The Trust issued Auction Preferred Shares (APS) on July 27, 2001 in a public offering. Dividends on the APS, which accrue daily, are cumulative at rates which are reset every seven days by an auction, unless a special dividend period has been set. Series of APS are identical in all respects except for the reset dates of the dividend rates. If the APS auctions do not successfully clear, the dividend payment rate over the next period for the APS holders is set at a specified maximum applicable rate until such time as the APS auctions are successful. Auctions have not cleared since February 13, 2008 and the rate since that date has been the maximum applicable rate (see Note 3). The maximum applicable rate on the APS is 125% of the “AA” Financial Composite Commercial Paper Rate at the date of the auction. The stated spread over the reference benchmark rate is determined based on the credit rating of the APS.

26

Eaton Vance

Senior Income Trust

December 31, 2022

Notes to Financial Statements (Unaudited) — continued

The number of APS issued and outstanding as of December 31, 2022 are as follows:

	APS Issued and Outstanding
Series A	752
Series B	752

The APS are redeemable at the option of the Trust at a redemption price equal to $25,000 per share, plus accumulated and unpaid dividends, on any dividend payment date. The APS are also subject to mandatory redemption at a redemption price equal to $25,000 per share, plus accumulated and unpaid dividends, if the Trust is in default for an extended period on its asset maintenance requirements with respect to the APS. If the dividends on the APS remain unpaid in an amount equal to two full years’ dividends, the holders of the APS as a class have the right to elect a majority of the Board of Trustees. In general, the holders of the APS and the common shares have equal voting rights of one vote per share, except that the holders of the APS, as a separate class, have the right to elect at least two members of the Board of Trustees. The APS have a liquidation preference of $25,000 per share, plus accumulated and unpaid dividends. The Trust is required to maintain certain asset coverage with respect to the APS as defined in the Trust's By-Laws and the 1940 Act. The Trust pays an annual fee up to 0.15% of the liquidation value of the APS to broker/dealers as a service fee if the auctions are unsuccessful; otherwise, the annual fee is 0.25%.

3  Distributions to Shareholders and Income Tax Information

The Trust intends to make monthly distributions of net investment income to common shareholders, after payment of any dividends on any outstanding APS. In addition, at least annually, the Trust intends to distribute all or substantially all of its net realized capital gains. Distributions to common shareholders are recorded on the ex-dividend date. Distributions to preferred shareholders are recorded daily and are payable at the end of each dividend period. The dividend rates for the APS at December 31, 2022, and the amount of dividends accrued (including capital gains, if any) to APS shareholders, average APS dividend rates (annualized), and dividend rate ranges for the six months then ended were as follows:

	APS Dividend Rates at December 31, 2022	Dividends Accrued to APS Shareholders	Average APS Dividend Rates	Dividend Rate Ranges (%)
Series A	5.42%	$341,109	3.60%	1.93-5.42
Series B	5.42	343,980	3.63	1.96-5.42

Beginning February 13, 2008 and consistent with the patterns in the broader market for auction-rate securities, the Trust's APS auctions were unsuccessful in clearing due to an imbalance of sell orders over bids to buy the APS. As a result, the dividend rates of the APS were reset to the maximum applicable rates. The table above reflects such maximum dividend rate for each series as of December 31, 2022.

Distributions to shareholders are determined in accordance with income tax regulations, which may differ from U.S. GAAP. As required by U.S. GAAP, only distributions in excess of tax basis earnings and profits are reported in the financial statements as a return of capital. Permanent differences between book and tax accounting relating to distributions are reclassified to paid-in capital. For tax purposes, distributions from short-term capital gains are considered to be from ordinary income.

At June 30, 2022, the Trust, for federal income tax purposes, had deferred capital losses of $17,363,755 which would reduce its taxable income arising from future net realized gains on investment transactions, if any, to the extent permitted by the Internal Revenue Code, and thus would reduce the amount of distributions to shareholders, which would otherwise be necessary to relieve the Trust of any liability for federal income or excise tax. The deferred capital losses are treated as arising on the first day of the Trust’s next taxable year and retain the same short-term or long-term character as when originally deferred. Of the deferred capital losses at June 30, 2022, $1,282,817 are short-term and $16,080,938 are long-term.

27

Eaton Vance

Senior Income Trust

December 31, 2022

Notes to Financial Statements (Unaudited) — continued

last day of the prior calendar year at market prices when shares are trading at a discount to net asset value. The share repurchase program does not obligate the Trust to purchase a specific amount of shares. There were no repurchases of common shares by the Trust for the six months ended December 31, 2022 and the year ended June 30, 2022.

Pursuant to a registration statement filed with the SEC, the Trust is authorized to issue up to an additional 4,551,438 common shares through an equity shelf offering program (the “shelf offering”). Under the shelf offering, the Trust, subject to market conditions, may raise additional capital from time to time and in varying amounts and offering methods at a net price at or above the Trust’s net asset value per common share. During the six months ended December 31, 2022 and the year ended June 30, 2022, there were no shares sold by the Trust pursuant to its shelf offering.

8  Financial Instruments

The Trust may trade in financial instruments with off-balance sheet risk in the normal course of its investing activities. These financial instruments may include forward foreign currency exchange contracts and may involve, to a varying degree, elements of risk in excess of the amounts recognized for financial statement purposes. The notional or contractual amounts of these instruments represent the investment the Trust has in particular classes of financial instruments and do not necessarily represent the amounts potentially subject to risk. The measurement of the risks associated with these instruments is meaningful only when all related and offsetting transactions are considered. A summary of obligations under these financial instruments at December 31, 2022 is included in the Portfolio of Investments. At December 31, 2022, the Trust had sufficient cash and/or securities to cover commitments under these contracts.

The Trust is subject to foreign exchange risk in the normal course of pursuing its investment objective. Because the Trust holds foreign currency denominated investments, the value of these investments and related receivables and payables may change due to future changes in foreign currency exchange rates. To hedge against this risk, the Trust enters into forward foreign currency exchange contracts.

The Trust enters into forward foreign currency exchange contracts that may contain provisions whereby the counterparty may terminate the contract under certain conditions, including but not limited to a decline in the Trust’s net assets below a certain level over a certain period of time, which would trigger a payment by the Trust for those derivatives in a liability position. At December 31, 2022, the fair value of derivatives with credit-related contingent features in a net liability position was $420,497. The aggregate fair value of assets pledged as collateral by the Trust for such liability was $630,000 at December 31, 2022.

The over-the-counter (OTC) derivatives in which the Trust invests are subject to the risk that the counterparty to the contract fails to perform its obligations under the contract.  To mitigate this risk, the Trust has entered into an International Swaps and Derivatives Association, Inc. Master Agreement (“ISDA Master Agreement”) or similar agreement with substantially all its derivative counterparties. An ISDA Master Agreement is a bilateral agreement between the Trust and a counterparty that governs certain OTC derivatives and typically contains, among other things, set-off provisions in the event of a default and/or termination event as defined under the relevant ISDA Master Agreement. Under an ISDA Master Agreement, the Trust may, under certain circumstances, offset with the counterparty certain derivative financial instruments’ payables and/or receivables with collateral held and/or posted and create one single net payment. The provisions of the ISDA Master Agreement typically permit a single net payment in the event of default including the

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Eaton Vance

Senior Income Trust

December 31, 2022

Notes to Financial Statements (Unaudited) — continued

bankruptcy or insolvency of the counterparty. However, bankruptcy or insolvency laws of a particular jurisdiction may impose restrictions on or prohibitions against the right of offset in bankruptcy or insolvency. Certain ISDA Master Agreements allow counterparties to OTC derivatives to terminate derivative contracts prior to maturity in the event the Trust’s net assets decline by a stated percentage or the Trust fails to meet the terms of its ISDA Master Agreements, which would cause the counterparty to accelerate payment by the Trust of any net liability owed to it.

The collateral requirements for derivatives traded under an ISDA Master Agreement are governed by a Credit Support Annex to the ISDA Master Agreement. Collateral requirements are determined at the close of business each day and are typically based on changes in market values for each transaction under an ISDA Master Agreement and netted into one amount for such agreement. Generally, the amount of collateral due from or to a counterparty is subject to a minimum transfer threshold amount before a transfer is required, which may vary by counterparty. Collateral pledged for the benefit of the Trust and/or counterparty is held in segregated accounts by the Trust’s custodian and cannot be sold, re-pledged, assigned or otherwise used while pledged. The portion of such collateral representing cash, if any, is reflected as deposits for derivatives collateral and, in the case of cash pledged by a counterparty for the benefit of the Trust, a corresponding liability on the Statement of Assets and Liabilities. Securities pledged by the Trust as collateral, if any, are identified as such in the Portfolio of Investments.

The fair value of open derivative instruments (not considered to be hedging instruments for accounting disclosure purposes) and whose primary underlying risk exposure is foreign exchange risk at December 31, 2022 was as follows:

	Fair Value
Derivative	Asset Derivative	Liability Derivative(1)
Forward foreign currency exchange contracts	$ —	$(420,497)

(1)	Statement of Assets and Liabilities location: Payable for open forward foreign currency exchange contracts.

The Trust's derivative liabilities at fair value by type, which are reported gross in the Statement of Assets and Liabilities, are presented in the table above. The following table presents the Trust's derivative liabilities by counterparty, net of amounts available for offset under a master netting agreement and net of the related collateral pledged by the Trust for such liabilities as of December 31, 2022.

(a)	In some instances, the total collateral pledged may be more than the amount shown due to overcollateralization.
(b)	Net amount represents the net amount payable to the counterparty in the event of default.

The effect of derivative instruments (not considered to be hedging instruments for accounting disclosure purposes) on the Statement of Operations and whose primary underlying risk exposure is foreign exchange risk for the six months ended December 31, 2022 was as follows:

(1)	Statement of Operations location: Net realized gain (loss) - Forward foreign currency exchange contracts.
(2)	Statement of Operations location: Change in unrealized appreciation (depreciation) - Forward foreign currency exchange contracts.

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Eaton Vance

Senior Income Trust

December 31, 2022

Notes to Financial Statements (Unaudited) — continued

The average notional amount of forward foreign currency exchange contracts (based on the absolute value of notional amounts of currency purchased and currency sold) outstanding during the six months ended December 31, 2022, which is indicative of the volume of this derivative type, was approximately $16,160,000.

9  Revolving Credit and Security Agreement

The Trust has entered into a Revolving Credit and Security Agreement, as amended (the Agreement) with conduit lenders and a bank to borrow up to $50 million. Borrowings under the Agreement are secured by the assets of the Trust. Interest is charged at a rate above the conduits’ commercial paper issuance rate and is payable monthly. Under the terms of the Agreement, in effect through March 6, 2023, the Trust also pays a program fee of 0.90% per annum on its outstanding borrowings to administer the facility and a liquidity fee of 0.15% (0.25% if the outstanding loan amount is less than or equal to 60% of the total facility size) per annum on the unused portion of the total commitment under the Agreement. Program and liquidity fees for the six months ended December 31, 2022 totaled $127,805 and are included in interest expense and fees on the Statement of Operations. In connection with the renewal of the Agreement on March 7, 2022, the Trust paid upfront fees of $75,000, which is being amortized to interest expense over a period of one year through March 6, 2023. The unamortized balance at December 31, 2022 is approximately $13,000 and is included in prepaid upfront fees on notes payable on the Statement of Assets and Liabilities. At December 31, 2022, the Trust had borrowings outstanding under the Agreement of $18,000,000 at an annual interest rate of 4.48%. Based on the short-term nature of the borrowings under the Agreement and the variable interest rate, the carrying amount of the borrowings at December 31, 2022 approximated its fair value. If measured at fair value, borrowings under the Agreement would have been considered as Level 2 in the fair value hierarchy (see Note 11) at December 31, 2022. For the six months ended December 31, 2022, the average borrowings under the Agreement and the average annual interest rate (excluding fees) were $19,239,130 and 2.96%, respectively.

Name	Value, beginning of period	Purchases	Sales proceeds	Net realized gain (loss)	Change in unrealized appreciation (depreciation)	Value, end of period	Dividend income	Shares, end of period
Short-Term Investments
Liquidity Fund	$2,499,592	$38,545,439	$(37,992,390)	$ —	$ —	$3,052,641	$32,850	3,052,641

11  Fair Value Measurements

Under generally accepted accounting principles for fair value measurements, a three-tier hierarchy to prioritize the assumptions, referred to as inputs, is used in valuation techniques to measure fair value. The three-tier hierarchy of inputs is summarized in the three broad levels listed below.

•	Level 1 – quoted prices in active markets for identical investments
•	Level 2 – other significant observable inputs (including quoted prices for similar investments, interest rates, prepayment speeds, credit risk, etc.)
•	Level 3 – significant unobservable inputs (including a fund's own assumptions in determining the fair value of investments)

In cases where the inputs used to measure fair value fall in different levels of the fair value hierarchy, the level disclosed is determined based on the lowest level input that is significant to the fair value measurement in its entirety. The inputs or methodology used for valuing securities are not necessarily an indication of the risk associated with investing in those securities.

At December 31, 2022, the hierarchy of inputs used in valuing the Trust’s investments and open derivative instruments, which are carried at value, were as follows:

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Eaton Vance

Senior Income Trust

December 31, 2022

Notes to Financial Statements (Unaudited) — continued

13  Additional Information

On August 27, 2020, Saba Capital Master Fund, Ltd., a hedge fund (“Saba”), filed claims against the Trust in a lawsuit in Suffolk County Superior Court in Massachusetts asserting breach of contract and fiduciary duty by the Trust and certain of its affiliates, the Trust's adviser, and the Board, following the implementation by the Trust of by-law amendments that (i) require trustee nominees in contested elections to obtain affirmative votes of a majority of eligible shares in order to be elected and (ii) establish certain requirements related to shares obtained in "Control Share Acquisitions". With respect to the Trust, Saba seeks rescission of these by-law provisions and certain related relief. On March 31, 2021, the court allowed in part and denied in part a motion to dismiss Saba's claims. Discovery is complete. On January 23, 2023, the court granted in part and denied in part motions for summary judgment filed by both the Board and Saba; the court denied the Board's motion as to the breach of contract claim, granted the Board's motion as to the claims for breach of fiduciary duty against the independent trustees, and granted Saba's motion as to the Control Share Amendment. While management of the Trust is unable to predict the outcome of this matter, it does not believe the outcome would result in the payment of any monetary damages by the Trust.

33

Eaton Vance

Senior Income Trust

December 31, 2022

Annual Meeting of Shareholders (Unaudited)

The Trust held its Annual Meeting of Shareholders on October 13, 2022. The following actions were taken by the shareholders.

Proposal 1a: The election of George J. Gorman and Marcus L. Smith as Class III Trustees of the Trust for a three-year term expiring in 2025.

The following votes were cast by the Trust’s common and APS shareholders, voting together as a single class:

Proposal 1b: The election of Nancy A. Wiser as a Class III Trustee of the Trust for a three-year term expiring in 2025.

The following votes were cast by the Trust’s APS shareholders, voting separately as a single class:

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Eaton Vance

Senior Income Trust

December 31, 2022

Officers and Trustees

Officers
Eric A. Stein President	Nicholas Di Lorenzo Secretary
Deidre E. Walsh Vice President and Chief Legal Officer	Richard F. Froio Chief Compliance Officer
James F. Kirchner Treasurer

Trustees

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Eaton Vance Funds

IMPORTANT NOTICES

Delivery of Shareholder Documents. The Securities and Exchange Commission (SEC) permits funds to deliver only one copy of shareholder documents, including prospectuses, proxy statements and shareholder reports, to fund investors with multiple accounts at the same residential or post office box address. This practice is often called “householding” and it helps eliminate duplicate mailings to shareholders. American Stock Transfer & Trust Company, LLC (“AST”), the closed-end funds transfer agent, or your financial intermediary, may household the mailing of your documents indefinitely unless you instruct AST, or your financial intermediary, otherwise. If you would prefer that your Eaton Vance documents not be householded, please contact AST or your financial intermediary. Your instructions that householding not apply to delivery of your Eaton Vance documents will typically be effective within 30 days of receipt by AST or your financial intermediary.

Portfolio Holdings. Each Eaton Vance Fund and its underlying Portfolio(s) (if applicable) files a schedule of portfolio holdings on Part F to Form N-PORT with the SEC. Certain information filed on Form N-PORT may be viewed on the Eaton Vance website at www.eatonvance.com, by calling Eaton Vance at 1-800-262-1122 or in the EDGAR database on the SEC’s website at www.sec.gov.

Proxy Voting. From time to time, funds are required to vote proxies related to the securities held by the funds. The Eaton Vance Funds or their underlying Portfolios (if applicable) vote proxies according to a set of policies and procedures approved by the Funds’ and Portfolios’ Boards. You may obtain a description of these policies and procedures and information on how the Funds or Portfolios voted proxies relating to portfolio securities during the most recent 12-month period ended June 30, without charge, upon request, by calling 1-800-262-1122 and by accessing the SEC’s website at www.sec.gov.

Share Repurchase Program. The Fund’s Board of Trustees has approved a share repurchase program authorizing the Fund to repurchase up to 10% of its common shares outstanding as of the last day of the prior calendar year in open-market transactions at a discount to net asset value. The repurchase program does not obligate the Fund to purchase a specific amount of shares. The Fund’s repurchase activity, including the number of shares purchased, average price and average discount to net asset value, is disclosed in the Fund’s annual and semi-annual reports to shareholders.

Additional Notice to Shareholders. If applicable, a Fund may also redeem or purchase its outstanding preferred shares in order to maintain compliance with regulatory requirements, borrowing or rating agency requirements or for other purposes as it deems appropriate or necessary.

Closed-End Fund Information. Eaton Vance closed-end funds make fund performance data and certain information about portfolio characteristics available on the Eaton Vance website shortly after the end of each month. Other information about the funds is available on the website. The funds’ net asset value per share is readily accessible on the Eaton Vance website. Portfolio holdings for the most recent month-end are also posted to the website approximately 30 days following the end of the month. This information is available at www.eatonvance.com on the fund information pages under “Closed-End Funds & Term Trusts.”

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Investment Adviser and Administrator

Eaton Vance Management
Two International Place
Boston, MA 02110

Custodian

State Street Bank and Trust Company
State Street Financial Center, One Lincoln Street
Boston, MA 02111

Transfer Agent

American Stock Transfer & Trust Company, LLC
6201 15^th Avenue
Brooklyn, NY 11219

Fund Offices

Two International Place
Boston, MA 02110

7700    12.31.22