Patent ID: 7906796

Claim:
A bipolar transistor including a base layer comprising a p-type semiconductor, a first emitter layer comprising an n-type semiconductor, and a second emitter layer comprising an n-type semiconductor with a donor density being higher compared with that of the first emitter layer are stacked successively, having a portion of the first emitter layer, the second emitter layer, and a surface passivation layer in a mesa structure, and having a base-contact region disposed to the periphery of the second emitter layer sandwiching a semiconductor region for suppressing recombination and connected electrically with the base layer, wherein the semiconductor region for suppressing recombination comprises an identical semiconductor having a donor density identical with that of the first emitter layer and is present in contact with the base layer and the surface passivation layer, and the width of the semiconductor region for suppressing recombination is equal with or longer than the electron diffusion length in the base layer.