A semiconductor device includes an insulating substrate having a ceramic substrate and metal coating layers on opposite surfaces of the ceramic substrate, a semiconductor chip mounted on one surface of the insulating substrate, a heat sink directly or indirectly fixed to the other surface of the insulating substrate and thermally connected to the semiconductor chip through the insulating substrate and at least one anti-warping sheet disposed on at least one surface of the heat sink. The anti-warping sheet is made of a metal sheet having a coating layer and has coefficient of thermal expansion between those of the insulating substrate and the heat sink.
