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ANNUAL REPORT PURSUANT TO SECTION 13 OR 15 ( d ) OF THE SECURITIES EXCHANGE ACT OF 1934 For the fiscal year ended December 31 , 2020 OR 0 TRANSITION REPORT PURSUANT TO SECTION 13 OR 15 ( d ) OF THE SECURITIES EXCHANGE ACT OF 1934 UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington , D.C. 20549 FORM 10 - K Delaware ( State or other jurisdiction of incorporation or organization ) For the transition period from to Commission File Number 001-36509 AMPHASTAR PHARMACEUTICALS , INC . ( Exact name of registrant as specified in its charter ) Large accelerated filer Non - accelerated filer 11570 6 Street Rancho Cucamonga , CA ( Address of principal executive offices ) Title of each class Common Stock , par value $ 0.0001 per share ■ ( 909 ) 980-9484 ( Registrant's telephone number , including area code ) Securities registered pursuant to Section 12 ( b ) of the Act : Trading Symbol ( s ) AMPH 33-0702205 ( I.R.S. Employer Identification No. ) 91730 ( zip code ) No X No 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 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 Name of each exchange on which registered The NASDAQ Stock Market LLC 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 . 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 is a shell company ( as defined in Rule 12b - 2 of the Act ) . Yes No The aggregate market value of the registrant's common stock held by non - affiliates of the registrant on June 30 , 2020 ( the last business day of the registrant's most recently completed second fiscal quarter ) , based upon the closing price of Common Stock on such date as reported by Nasdaq Global Select Market , was approximately $ 566,686,688 . Shares of common stock known to be held by directors , executive officers and holders of 5 % or more of the outstanding common stock of the registrant are not included in the computation . No determination has been made that such persons are " affiliates " of the registrant for any other purpose . At March 8 , 2021 , there were 47,432,937 shares of the registrant's common stock outstanding . X 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 Documents Incorporated by Reference Portions of the registrant's definitive proxy statement to be filed with the Securities and Exchange Commission within 120 days after the end of its fiscal year to which this report relates in connection with its 2021 Annual Meeting of Stockholders are incorporated by reference into Part III hereof . |