A method of fabricating an integrated BiCMOS circuit is provided, the circuit including bipolar transistors 10 and CMOS transistors 12 on a substrate. The method comprises the step of forming an epitaxial layer 28 to form a channel region of a MOS transistor and a base region of a bipolar transistor. Growing of the epitaxial layer includes growing a first sublayer of silicon 28a, a first sublayer of silicon-germanium 28b onto the first sublayer of silicon, a second sublayer of silicon 28c onto the first sublayer of silicon-germanium, and a second sublayer of silicon-germanium 28d onto the second sublayer of silicon. Furthermore, an integrated BiCMOS circuit is provided, which includes an epitaxial layer 28 as described above.