UNITED STATES SECURITIES AND EXCHANGE COMMISSION WASHINGTON, DC 20549 Form 10-K (Mark One) ☒ ANNUAL REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the fiscal year ended September 30, 2020 or ☐ TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the transition period from to Commission file number: 814-00794 GOLUB CAPITAL BDC, INC. (Exact Name of Registrant as Specified in its Charter) Delaware 27-2326940 (State or Other Jurisdiction of (I.R.S. Employer Incorporation or Organization) Identification No.) 200 Park Avenue, 25th Floor, New York, NY 10166 (Address of Principal Executive Offices) (Zip Code) (212) 750-6060 (Registrant’s Telephone Number, Including Area Code) Securities registered pursuant to Section 12(b) of the Act: Title of each class Trading Symbol Name of each exchange on which registered Common Stock, par value $0.001 per share GBDC The Nasdaq Global Select Market Securities registered pursuant to Section 12(g) of the Act: None Indicate by check mark if the registrant is a well-known seasoned issuer, as defined in Rule 405 of the Securities Act. Yes ☐ No ☒ Indicate by check mark if the registrant is not required to file reports pursuant to Section 13 or 15(d) of the Act. Yes ☐ No ☒ Indicate by check mark whether the registrant: (1) has filed all reports required to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during the preceding 12 months (or for such shorter period that the registrant was required to file such reports), and (2) has been subject to such filing requirements for the past 90 days. Yes ☒ No ☐ Indicate by check mark whether the registrant has submitted electronically every Interactive Data File required to be submitted pursuant to Rule 405 of Regulation S-T (§232.405 of this chapter) during the preceding 12 months (or for such shorter period that the registrant was required to submit such files). Yes ☐ No ☒ Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer or a smaller reporting company. See definitions of “large accelerated filer”, “accelerated filer” and “smaller reporting company” in Rule 12b-2 of the Exchange Act. (Check one): Large accelerated filer ☒ Accelerated filer ☐ Non-accelerated filer ☐ Smaller reporting company ☐ Emerging growth company ☐ If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act. ☐ Indicate by check mark whether the registrant has filed a report on and attestation to its management’s assessment of the effectiveness of its internal control over financial reporting under Section 404(b) of the Sarbanes-Oxley Act (15 U.S.C. 7262(b)) by the registered public accounting firm that prepared or issued its audit report. Yes ☒ No ☐ Indicate by check mark whether the registrant is a shell company (as defined in Rule 12b-2 of the Securities Exchange Act of 1934). Yes ☐ No ☒ The aggregate market value of common stock held by non-affiliates of the registrant on March 31, 2020 was approximately $1,597.2 million. For the purposes of calculating this amount only, all directors and executive officers of the registrant have been treated as affiliates. There were 167,259,511 shares of the registrant’s common stock outstanding as of November 30, 2020. DOCUMENTS INCORPORATED BY REFERENCE Portions of the registrant’s proxy statement to be filed with the Securities and Exchange Commission pursuant to Regulation 14A in connection with the registrant’s 2021 Annual Meeting of Stockholders, which will be filed subsequent to the date hereof, are incorporated by reference into Part III of this Form 10-K. Such proxy statement will be filed with the Securities and Exchange Commission not later than 120 days following the end of the registrant’s fiscal year ended September 30, 2020. Part I. Item 1. Business ...................................................... 5 Item 1A. Risk Factors ................................................... 38 Item 1B. Unresolved Staff Comments ........................................ 82 Item 2. Properties ..................................................... 83 Item 3. Legal Proceedings ............................................... 83 Item 4. Mine Safety Disclosures ........................................... 83 Part II. Item 5. Market for Registrant’s Common Equity, Related Stockholder Matters and Issuer Purchases of Equity Securities ...................................... 84 Item 6. Selected Consolidated Financial Data ................................. 86 Item 7. Management’s Discussion and Analysis of Financial Condition and Results of Operations .................................................... 88 Item 7A. Quantitative and Qualitative Disclosures about Market Risk . ................ 124 Item 8. Consolidated Financial Statements and Supplementary Data ................. 125 Item 9. Changes in and Disagreements with Accountants on Accounting and Financial Disclosure .................................................... 257 Item 9A. Controls and Procedures .......................................... 257 Item 9B. Other Information ............................................... 257 Part III. Item 10. Directors, Executive Officers and Corporate Governance .................... 258 Item 11. Executive Compensation .......................................... 258 Item 12. Security Ownership of Certain Beneficial Owners and Management and Related Stockholder Matters ............................................. 258 Item 13. Certain Relationships and Related Transactions, and Director Independence . ..... 258 Item 14. Principal Accountant Fees and Services ................................ 258 Part IV. Item 15. Exhibits and Financial Statement Schedules ............................. 259 Signatures ..................................................... 265 i PART I In this annual report on Form 10-K, except as otherwise indicated, the terms: • “we,” “us,” “our” and “Golub Capital BDC” refer to Golub Capital BDC, Inc., a Delaware corporation, and its consolidated subsidiaries; • “Holdings” refers to Golub Capital BDC Holdings LLC, a Delaware limited liability company, or LLC, our direct subsidiary; • “GCIC Holdings” refers to GCIC Holdings LLC, a Delaware LLC, our direct subsidiary; • “2014 Issuer” refers to Golub Capital BDC CLO 2014 LLC, a Delaware LLC, our direct subsidiary; • “2018 Issuer” refers to Golub Capital BDC CLO III LLC, a Delaware LLC, our indirect subsidiary; • “GCIC 2018 Issuer” refers to GCIC CLO II LLC, a Delaware LLC, our indirect subsidiary; • “2020 Issuer” refers to Golub Capital BDC CLO 4 LLC, a Delaware LLC, our indirect subsidiary; • “2018 CLO Depositor” refers to Golub Capital BDC CLO III Depositor LLC, a Delaware LLC, our direct subsidiary; • “GCIC CLO Depositor” refers to GCIC CLO II Depositor LLC, a Delaware LLC, our direct subsidiary; • “2020 CLO Depositor” refers to Golub Capital BDC CLO 4 Depositor LLC, a Delaware LLC, our direct subsidiary; • “Controlling Class” refers to the most senior class of notes then outstanding of the 2014 Issuer, 2018 Issuer, GCIC 2018 Issuer or the 2020 Issuer, as applicable; • “Funding” refers to Golub Capital BDC Funding LLC, a Delaware LLC, our direct subsidiary; • “Funding II” refers to Golub Capital BDC Funding II LLC, a Delaware LLC, our direct subsidiary; • “Funding Subsidiaries” refers, collectively, to, prior to termination on the Credit Facility on February 4, 2019, Funding, Funding II, GCIC Funding, GCIC Funding II and each, a “Funding Subsidiary”; • “GCIC Funding” refers to GCIC Funding LLC, a Delaware LLC, our direct subsidiary; • “GCIC Funding II” refers to GCIC Funding II LLC, a Delaware LLC, our direct subsidiary; • “Merger Sub” refers to Fifth Ave Subsidiary Inc., our wholly owned subsidiary; • “GCIC” refers to Golub Capital Investment Corporation, a Maryland corporation that we acquired on September 16, 2019 pursuant to an agreement and plan of merger by and among us, GCIC, GC Advisors, and for certain limited purposes our Administrator, or, as amended, the Merger Agreement; prior to such acquisition, which we refer to as the Merger, GCIC was an externally managed, closed-end, non-diversified management investment company that elected to be regulated as a business development company under the Investment Company Act of 1940, as amended, or the 1940 Act, and whose investment adviser was GC Advisors; • “2014 Debt Securitization” refers to the $402.6 million term debt securitization that we completed on June 5, 2014, as most recently amended on March 23, 2018 and redeemed on August 26, 2020, in which the 2014 Issuer issued an aggregate of $402.6 million of notes, or the “2014 Notes,” including $191.0 million of Class A-1-R 2014 Notes, which bore interest at a rate of three-month LIBOR, plus 0.95%, $20.0 million of Class A-2-R 2014 Notes, which bore interest at a rate of three-month LIBOR plus 0.95%, $35.0 million of Class B-R 2014 Notes, which bore interest at a rate of three-month LIBOR plus 1.40%, $37.5 million of Class C-R 2014 Notes, which bore interest at a rate of three-month LIBOR plus 1.55%, and $119.1 million of membership interests that did not bear interest; • “2018 Debt Securitization” refers to the $602.4 million term debt securitization that we completed on November 16, 2018, in which the 2018 Issuer issued an aggregate of $602.4