A semiconductor device that reduces the deformation of a metal base due to pressure during transfer molding, to thereby suppress the occurrence of cracks in an insulating layer to achieve high electrical reliability. The semiconductor device includes: a metal member provided, on its lower surface, with a projection and a depression, and a projecting peripheral portion surrounding the projection and the depression and having a height greater than or equal to a height of the projection of the projection and the depression; an insulating layer formed on an upper surface of the metal member; a metal layer formed on an upper surface of the insulating layer; a semiconductor element joined to an upper surface of the metal layer; and a sealing resin to seal the semiconductor element, the metal layer, the insulating layer and the metal member.