The formation of &bgr;‐SiC during rapid thermal chemical vapor deposition of an epitaxial Si layer on a (100) Si substrate has been demonstrated using high‐resolution cross‐sectional transmission electron microscopy and secondary ion mass spectrometry (SIMS) depth profiling. Ellipsoidal &bgr;‐SiC precipitates (3×10 nm2average size) were found with a density of (6±1)×109cm−2along the epilayer/substrate interface. SIMS revealed about 0.2 monolayer of carbon concentrated at the interface. The precipitates were shown to form during the hydrogen prebake as a result of improper surface cleaning. The crystalline quality of the epitaxial layer, however, was unaffected by the presence of the &bgr;‐SiC.