We report on the role of hydrogen surface passivation in achieving low-temperature silicon epitaxy by chemical vapor deposition processes. Upon insertion of an HF-etched silicon wafer into an epitaxial silicon deposition apparatus, residual contamination of the Si surface is negligible. Si 2p core level photoemission spectra demonstrate that the silicon surface is stable in air and free of SiO2 for a time period of minutes. The predominant passivating species is found to be silicon hydride. We demonstrate that hydrogen passivation by HF pretreatment leads to two divergent temperature ranges where epitaxy is successful, those being a low-temperature range, 425≲T≲ 650°C, and a high-temperature regime, T≳750°C. Additionally, we employ temperature-programmed desorption techniques to elucidate the role of hydrogen in the transition to a steady-state growth process, employing ultrahigh vacuum/chemical vapor deposition as the model system.