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UNITED STATES SECURITIES AND EXCHANGE COMMISSION WASHINGTON , D.C. 20549 FORM 40 - F ( Check One ) ☐ REGISTRATION STATEMENT PURSUANT TO SECTION 12 OF THE SECURITIES EXCHANGE ACT OF 1934 ☑ ANNUAL REPORT PURSUANT TO SECTION 13 ( A ) OR 15 ( D ) OF THE SECURITIES EXCHANGE ACT OF 1934 For the fiscal year ended : December 31 , 2020 Commission file number : 001-33414 DENISON MINES CORP . ( Exact name of registrant as specified in its charter ) Ontario , Canada ( Province or other jurisdiction of incorporation or organization ) 1090 ( Primary standard industrial classification code number ) 98-0622284 ( I.R.S. employer identification number ) 1100 - 40 University Avenue , Toronto , Ontario M5J 1T1 Canada ; Phone number : 416-979-1991 ( Address and telephone number of registrant's principal executive offices ) CT Corporation System 28 Liberty Street New York , NY 10005 Phone number : 212-894-8940 ( Name , address and telephone number of agent for service in the United States ) Securities registered pursuant to Section 12 ( b ) of the Act : Not applicable . Securities registered pursuant to Section 12 ( g ) of the Act : Common shares without par value .