A bipolar transistor is supported by a single-crystal silicon substrate including a collector contact region. A first epitaxial region forms a collector region of a first conductivity type on the collector contact region. A second epitaxial region forms a base region of a second conductivity type. Deposited semiconductor material forms an emitter region of the first conductivity type. The collector region, base region and emitter region are located within an opening having sidewalls lined with an insulating sheath. A portion of the insulating sheath adjacent the base region is removed and a base contact region is formed by epitaxial material grown from a portion of the base region exposed by removal of the portion of the insulating sheath.