An n+-emitter layer arranged under an emitter electrode is formed of convex portions arranged at predetermined intervals and a main body coupled to the convex portions. A convex portion region is in contact with the emitter electrode, and a p+-layer doped more heavily than a p-base layer is arranged at least below the emitter layer. In a power transistor of a lateral structure, a latch-up immunity of a parasitic thyristor can be improved, and a turn-off time can be reduced.