The first reported self-aligned heterojunction bipolar transistor (HBT) in silicon technology is presented. A SiGe epitaxial base is integrated in a structure which uses in-situ doped epitaxial lateral overgrowth for the formation of the emitter window and the extrinsic base contact. Nearly ideal I- V characteristics have been achieved for a base width of 60 nm with an intrinsic base resistance of 4.6 kΩ/∓ and for emitter widths down to 0.4 μm. A dc collector current enhancement factor of 3.1 was obtained relative to a Si homojunction transistor with a 1.25 times higher intrinsic base resistance. The breakdown voltage BVCBO is identical for both Si and SiGe devices, even though the collector-base (C-B) depletion region is partly overlapped with the reduced-bandgap SiGe strained layer. The lower BVCE0, measured for the SiGe-base transistor, is due to the higher current gain. Based on these results the fabrication of high-speed bipolar circuits that take advantage of SiGe-base bandgap engineering seems possible using selective epitaxy emitter window (SEEW) technology.