The present disclosure relates to semiconductor structures and, more particularly, to a heterojunction bipolar transistor and methods of manufacture. The structure includes: a sub-collector region; a collector region above the sub-collector region; an intrinsic base region composed of intrinsic base material located above the collector region; an emitter located above and separated from the intrinsic base material; and a raised extrinsic base having a stepped configuration and separated from and self-aligned to the emitter.