A semiconductor device includes an N-type semiconductor substrate comprising silicon, an N-type low-concentration impurity layer that is in contact with the upper surface of the N-type semiconductor substrate, a metal layer that is in contact with the entire lower surface of the N-type semiconductor substrate and has a thickness of at least 20 μm, and first and second vertical MOS transistors formed in the low-concentration impurity layer. The ratio of the thickness of the metal layer to the thickness of a semiconductor layer containing the N-type semiconductor substrate and the low-concentration impurity layer is greater than 0.27. The semiconductor device further includes a support comprising a ceramic material and bonded to the entire lower surface of the metal layer only via a bonding layer.