Abstract: A heterojunction bipolar transistor includes a substrate, a semiconductor unit, an electrode unit and a dielectric layer. The semiconductor unit includes a collector layer, a base layer and an emitter layer sequentially formed on the substrate in such order. The electrode unit includes a collector electrode, a base electrode, and an emitter electrode respectively disposed on the collector layer, the base layer and the emitter layer. The dielectric layer covers and cooperates with the emitter layer to define an opening extending therethrough and terminating at the base layer to expose a contact region. The base electrode is disposed on the contact region, extends through the opening, and partially covers the dielectric layer.