A semiconductor device is provided which comprises a connecting lead 4 mounted between a MOS-FET 1 and a regulatory IC 2 on a support plate 3. Connecting lead 4 has a thermally radiative and electrically conductive substrate 6 and electrically insulative and thermal transfer-resistive covering 7. Substrate 6 has one end 6a providing one main surface 4a of connecting lead 4 which is mounted and electrically connected on the other main surface 1b of MOS-FET 1. Covering 7 provides the other main surface 4b of connecting lead 4 for supporting regulatory IC 2 at one end 6a of substrate 6. When electric current flow is supplied to MOS-FET 1 through an electrified path of support plate 3 and substrate of connecting lead 4, heat produced from operating MOS-FET 4 is effectively radiated through support plate 3 and substrate 6 of connecting lead 4 to improve thermal radiation in the semiconductor device in the layered structure of the semiconducting elements while heavy current can flow through MOS-FET 1 due to sufficient heat radiation.