Abstract: A horizontal heterojunction bipolar transistor (HBT) includes doped single crystalline Ge having a doping of the first conductivity type as the base having an energy bandgap of about 0.66 eV, and doped polysilicon having a doping of a second conductivity type as a wide-gap-emitter having an energy bandgap of about 1.12 eV. In one embodiment, doped polysilicon having a doping of the second conductivity type is employed as the collector. In other embodiments, a single crystalline Ge having a doping of the second conductivity type is employed as the collector. In such embodiments, because the base and the collector include the same semiconductor material, i.e., Ge, having the same lattice constant, there is no lattice mismatch issue between the collector and the base. In both embodiments, because the emitter is polycrystalline and the base is single crystalline, there is no lattice mismatch issue between the base and the emitter.