A semiconductor device includes a semiconductor chip that generates heat in operation, a pair of heat sinks for cooling the chip, and a mold resin, in which the chip and the heat sinks are embedded. The thickness t1 of the chip and the thickness t2 of one of heat sinks that is joined to the chip using a solder satisfy the equation of t2/t1.gtoreq.5. Furthermore, the thermal expansion coefficient .alpha.1 of the heat sinks and the thermal expansion coefficient .alpha.2 of the mold resin satisfy the equation of 0.5.ltoreq..alpha.2/.alpha.1.ltoreq.1.5. In addition, the surface of the chip that faces the solder has a roughness Ra that satisfies the equation of Ra.ltoreq.500 nm. Moreover, the solder is a Sn-based solder to suppress relaxation of a compressive stress in the chip, which is caused by the creeping of the solder.