A semiconductor device chip holder which has a plurality of plates laminated together, each having a different thermal expansion coefficient. A semiconductor chip is mounted on the upper surface of the chip holder, and molding resin is disposed only on the upper side of the chip holder encapsulating the semiconductor chip. At high temperatures the bimetal effect due to this construction causes the chip holder to warp, which generates a stress acting on the semiconductor chip compressing it. The piezoresistance effect thus obtained reduces the on-resistance of the semiconductor chip, thereby enabling the device to exhibit a stable and low on-resistance over a wide temperature range.