Abstract: A method of fabricating an HBT using differential epitaxy. By using an emitter mask and an exside-inside spacer structure, a self-aligned fabrication of an emitter contact and a base contact is carried out. The emitter contact layer is made from amorphous silicon. Since the entire process sequence is very temperature-stable and can be carried out at lower implantation energies than conventional methods, HBT's having a high layer quality can be fabricated by the method of the invention which is suitable for mass production and with which high oscillation frequencies can be accomplished.