Abstract: 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 formed in a stack of insulating layers that includes a sacrificial layer. The sacrificial layer is selectively removed to expose a side wall of the base region. Epitaxial growth from the exposed sidewall forms a base contact region.