A semiconductor device includes: a semiconductor substrate; a heat sink mounted on an upper surface of the semiconductor substrate; wirings formed on a lower surface of the semiconductor substrate; and the like. The heat sink is mounted on the upper surface of the semiconductor substrate, and a planar size thereof is approximately the same as that of the semiconductor substrate. Moreover, the heat sink has a thickness of 500 μm to 2 mm, and may be formed to be thicker than the semiconductor substrate. By using the heat sink to reinforce the substrate, a thickness of the semiconductor substrate can be reduced to, for example, about 50 μm. As a result, a thickness of the entire semiconductor device can be reduced.