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TABLE OF CONTENTS ( Mark One ) X UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington , D.C. 20549 FORM 10 - K No X ANNUAL REPORT PURSUANT TO SECTION 13 OR 15 ( d ) OF THE SECURITIES EXCHANGE ACT OF 1934 No X For the fiscal year ended December 31 , 2020 OR TRANSITION REPORT PURSUANT TO SECTION 13 OR 15 ( d ) OF THE SECURITIES EXCHANGE ACT OF 1934 Title of each class Common Stock , par value $ 0.001 per share Commission file number : 814-01175 BAIN CAPITAL SPECIALTY FINANCE , INC . ( Exact Name of Registrant as Specified in its Charter ) Delaware ( State or Other Jurisdiction of Incorporation or Organization ) 200 Clarendon Street , 37th Floor Boston , MA ( Address of Principal Executive Office ) ( 617 ) 516-2000 ( Registrant's Telephone Number , Including Area Code ) Securities registered pursuant to Section 12 ( b ) of the Act : Trading Symbol ( s ) 81-2878769 ( I.R.S. Employer Identification No. ) BCSF 02116 ( Zip Code ) 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 Indicate by check mark if the registrant is not required to file reports pursuant to Section 13 or Section 15 ( d ) of the Act . Yes 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 Name of each exchange on which registered New York Stock Exchange Indicate by check mark whether the registrant has submitted electronically , and 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 , a smaller reporting company or an emerging growth company . See the definitions of " large accelerated filer , " " accelerated filer , " " smaller reporting company " and " emerging growth company " in Rule 12b - 2 of the Exchange Act . Large accelerated filer > Non - accelerated filer 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 . Indicate by check mark whether the registrant is a shell company ( as defined in Rule 12b - 2 of the Act ) . Yes No The aggregate market value of the voting and non - voting common equity held by non - affiliates of the registrant , was $ 556.2 million based on the number of shares held by non - affiliates of the registrant as of June 30 , 2020 ( the last business day of the registrant's mostly recently completed second fiscal quarter ) . Shares of the registrant's common stock held by each executive officer , director and holder of 5 % or more of the outstanding common stock have been excluded in that such persons may be deemed to be affiliates . This calculation does not reflect a determination that certain persons are affiliates of the registrant for any other purpose . As of February 24 , 2021 , there were 64,562,265.27 shares of common stock outstanding . Documents Incorporated by Reference Portions of the registrant's definitive 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 where indicated . Such definitive 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 December 31 , 2020 .