Fabricating an integrated bipolar complementary metal oxide semiconductor (BiCMOS) circuit comprises forming an epitaxial layer (28) to form a channel region of a metal oxide semiconductor (MOS) transistor and a base region of a bipolar transistor. Forming the epitaxial layer includes sequentially epitaxially growing a sublayer of silicon, a sublayer of silicon-germanium, another sublayer of silicon, and another sublayer of silicon-germanium. The concentration of germanium in the first silicon-germanium sublayer is lower than in the second silicon-germanium sublayer. An independent claim is included for a BiCMOS integrated circuit including bipolar transistors and CMOS transistors on a substrate (14).
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