Heterojunction bipolar transistor and method for forming the same

A heterojunction bipolar transistor includes an emitter layer on a base layer on a collector layer on an upper sub-collector layer over a bottom sub-collector layer, a first dielectric film over the bottom sub-collector layer, the base layer and the emitter layer, a base electrode on the first dielectric film, electrically connected to the base layer through at least one first via hole in the first dielectric film, a second dielectric film on the first dielectric film and the base electrode, and a conductive layer on the second dielectric film, with conductive layer electrically connected to base electrode through a second via hole disposed in the second dielectric film, first dielectric film between the base electrode and first sidewall of a stack including the base layer and the collector layer, and second via hole laterally separated from the base layer.