A semiconductor device that includes a metal substrate including a top surface, a bottom surface and four side surfaces, a conductive pattern insulated from the metal substrate, and a semiconductor element mounted on and electrically connected to the conductive pattern. The top surface is insulated. Each of the side surfaces of the metal substrate includes a first inclining side surface and a second inclining side surface so as to form a convex shape protruding outwardly between the top surface and the bottom surface of the metal substrate, and the first inclining side surfaces of a pair of two opposing side surfaces are smaller than corresponding first inclining side surfaces of another pair of two opposing side surfaces.