We report the deposition of epitaxial films of GexSi1−xon (100) silicon by the ultrahigh vacuum chemical vapor deposition technique. Epitaxial films grown at temperatures ranging from 577 to 665 °C have been characterized with respect to growth rate and germanium content. The results show features which have not been previously reported including an incubation time and a peak in the growth rate as a function of GeH4/H2flow.