A thermal resistor is a metal body having a contact surface to be partially in contact to form a void and is electrically conductive as a whole. The thermal body may be a layered body having a plurality of metal bodies layered so as to be partially in contact with one another to form a void between them, or a metal body having a plurality of convex and concave portions on the surface, or a metal body formed by a plurality of metal plates each having a plurality of creases and layered so that the creases of the adjacent metal plates intersect, or a layered metal body formed by metal plates each having elasticity in the thickness direction and having elasticity in the layered direction as a whole, or metal body having a film formed by a different metal. Also disclosed in a semiconductor device having the thermal resistor inserted between a heating semiconductor element and a case cover and between a heat spreader and the case cover. Also disclosed is an electric device using the device.