A semiconductor device with superior long-term reliability is disclosed that alleviates current concentration into a switch structure arranged at an outermost portion. The semiconductor device comprises hetero semiconductor regions formed of polycrystalline silicon having a band gap width different from that of a drift region and hetero-adjoined with the drift region, a gate insulation film, a gate electrode adjoined to the gate insulation film, a source electrode connected to a source contact portion of the hetero semiconductor regions and an outermost switch structure and a repeating portion switch structure with a drain electrode connected to a substrate region. In a conduction state, the outermost switch structure comprises a mechanism in which the current flowing at the outermost switch structure becomes smaller than the current flowing at the repeating portion switch structure.