A semiconductor apparatus adhesive composition having excellent adhesion properties when pressure-bonded and has excellent connection reliability and insulation reliability when hardened and an adhesive sheet using this adhesive composition. An adhesive composition including: (A) a silicone resin constituted of a repeating unit represented by the following general formula (1); (B) a thermosetting resin; and (C) a compound having a flux activity, where R1 to R4 represent univalent hydrocarbon groups having carbon numbers from 1 to 8, which are equal to or different from each other; each of l and m is an integer from 1 to 100; each of a, b, c, and d is 0 or a positive number and meets 0