A semiconductor device includes a semiconductor module having a wiring board, semiconductor assemblies that include a multilayer substrate on which semiconductor elements are mounted, and a sealing part; a cooler; and a heat conduction sheet which is placed between the semiconductor module and the mounting surface of the cooler and which is in contact with the bottom surfaces of the multilayer substrates. The heat conduction sheet has recesses corresponding to at least parts of the outer edges of second electrically conductive plates provided on the bottoms of the multilayer substrates.