A semiconductor device is provided with a heat dissipating face side skirt portion, which is a frame-form projection, on a heat dissipating face of a lead frame. Because of this, creepage distance increases with a small increase in an amount of resin, and insulating properties improve. Also, the heat dissipating face side skirt portion is molded via two transfer molding steps, wettability of the second molding resin with respect to a first molding resin and the lead frame increases, and adhesion improves. Furthermore, an end face of an inner lead is exposed in an element sealing portion on a mounting face side, and covered with a second thin molded portion molded using the second molding resin, whereby heat generated in a semiconductor element can efficiently be caused to escape from faces of both a first thin molded portion and the second thin molded portion, because of which heat dissipation improves.