A semiconductor device including a board having a ground electrode and resin layers and a semiconductor chip mounted on the board, includes: a core embedded inside the board such that a front surface thereof is exposed on the front surface side of the board; a filled via provided so as to penetrate the resin layer disposed between the core and the ground electrode, of the resin layers, and electrically connecting a back surface of the core and the ground electrode; a joining material including a lid provided on the board so as to cover the semiconductor chip, having an exposed front surface, and having a high thermal conductivity and sintered silver joining a back surface of the lid and the front surface of the core; and a mold resin transfer-molded on an entirety of the front surface of the board and provided so as to surround the lid.