Abstract: A heterojunction bipolar transistor includes a collector layer, a base layer, an emitter layer, and a semiconductor layer that are laminated in this order, wherein the emitter layer includes a first region having an upper surface on which the semiconductor layer is laminated, and a second region being adjacent to the first region and having an upper surface that is exposed, and the first and second regions of the emitter layer have higher doping concentrations in portions near the upper surfaces than in portions near an interface between the emitter layer and the base layer.