Patent ID: 7838926

Claim:
A semiconductor device comprising: a semiconductor substrate having an upper surface and a lower surface opposed to each other; a first base region of a first conductivity type provided in the semiconductor substrate; a buffer region of the first conductivity type provided on a lower surface of the first base region and having an impurity concentration higher than an impurity concentration of the first base region; an emitter region of a second conductivity type provided on a lower surface of the buffer region; a second base region of the second conductivity type selectively provided on an upper surface of the first base region; a diffusion region of the first conductivity type selectively provided on an upper surface of the second base region; a control electrode provided in a region ranging from the diffusion region to the first base region via the second base region, with an insulating film therearound; a first main electrode provided to be electrically connected to the second base region and the diffusion region; and a second main electrode provided to be electrically connected to a lower surface of the emitter region, a junction interface between the buffer region and the first base region having a concave portion and a convex portion.