A semiconductor device which improves heat radiation performance and realizes size reduction and enables heat to be radiated swiftly from both of the principal surfaces of a semiconductor chip even when the semiconductor chip has a construction vulnerable to stresses. It comprises several IGBT chips each having a collector electrode on one principal surface and an emitter electrode and a gate electrode on the other principal surface and two high thermal conductivity insulating substrates sandwiching these IGBT chips and having electrode patterns for bonding to the electrodes of the IGBT chips disposed on their sandwiching surfaces, the electrodes of the IGBT chips and the electrode patterns of the high thermal conductivity insulating substrates being bonded by brazing.