Abstract: A semiconductor device includes a bipolar transistor formed on a semiconductor substrate 1, in which a collector region 13 is formed on the semiconductor substrate 1; a first insulating layer 31 having a first opening 51 formed in a collector region 13 is formed on the surface of the semiconductor substrate 1; and a base semiconductor layer 14B is formed in contact with the collector region through the first opening 51. The base semiconductor layer 14B is formed such that the edge thereof extends onto the first insulating layer 31.