Provided are a heterojunction bipolar transistor (HBT), a radio frequency module, and a communication device. The HBT includes: a semiconductor stack, an emitter metal, a first passivation layer, a first metal, and a dielectric layer. The semiconductor stack has first surface and second surfaces, and includes an emitter step and a base step having a step side surface. The emitter metal is disposed on the emitter step. The first passivation layer covers at least a side surface of the emitter metal and extends to cover a portion of the first surface exposed outside the emitter step, the step side surface, and a portion of the first surface exposed outside the base step. The first metal includes a base metal, which is at least partially disposed on the first surface, and is adjacent to the emitter step and spaced apart from the emitter step.

The disclosure provides bipolar transistor structures with a semiconductor film, and related methods. A structure of the disclosure includes an intrinsic base on a collector. The collector has a first doping type. A semiconductor film is on the intrinsic base and horizontally surrounds the intrinsic base. The semiconductor film horizontally encapsulates the intrinsic base. An emitter having the first doping type is on a first portion of the semiconductor film. An extrinsic base having a second doping type is on a second portion of the semiconductor film.