A semiconductor device includes an insulating substrate,a semiconductor element disposed on an upper surface of the substrate, a heat dissipation member, and a metal bonding layer that bonds the lower surface of the substrate to the upper surface of the heat dissipation member, and the area of the upper surface of the heat dissipation member is larger than the area of the lower surface of the substrate, and the metal bonding layer contacts the whole of the lower surface of the substrate and has an area larger than the area of the lower surface of the substrate, and the heat conductivity of the metal bonding layer is higher than the heat conductivity of the heat dissipation member.