Epitaxial silicon has been grown on Si(100) wafers using SiH4 in a rapid thermal chemical vapor deposition reactor in the temperature regime from 450–700 °C. Gas analysis during growth and thermal desorption spectra (TDS) after growth were measured with a differentially pumped mass spectrometer. We have attempted to estimate the surface population of hydrogen during epitaxial growth by ‘‘freezing out’’ the surface hydrogen with a rapid cool down and pump down followed by a temperature programmed desorption taken in the reactor. SiH is found as the majority species in equilibrium during growth, with the surface population decreasing from one monolayer around 550–600 °C, at a pressure of three mTorr SiH4. Molecular hydrogen does not interfere with silane adsorption in this pressure regime.