A semiconductor device having a plurality of semiconductor chips mounted on lead frames is miniaturized by reducing its planar size and thickness. By disposing a rear surface of a first island and a top surface of a second island so as to at least partially overlap each other, a first semiconductor chip on the first island and a second semiconductor chip on a rear surface of the second island are configured so as to overlap each other. Accordingly, a planar occupied area can be set smaller than planar areas of both of the chips. Moreover, thin metal wires to be connected to the second semiconductor chip are extended to a back side. Consequently, a thickness of a semiconductor device can also be reduced.