The deposition of epitaxial silicon films at temperatures from 600°–800°C by both very low-pressure chemical vapor deposition (VLPCVD) and plasma-enhanced chemical vapor deposition (PECVD) has been examined. The VLPCVD deposition process is first order in silane partial pressure, zero order in hydrogen partial pressure, and exhibits a low, 8–12 kcal/mole, activation energy for temperatures from 700°–800°C with 1–15 mtorr silane and hydrogen. For temperatures below 700°C an activation energy of 40 kcal/mole is observed. The growth rate depends upon surface orientation, decreasing in the order (100), (111), polycrystalline, indicating surface processes are rate controlling. The low activation energy regime is associated with a process controlled by silane adsorption and decomposition on a sparsely covered silicon surface. The higher activation energy regime is thought to reflect growth under conditions of high surface coverage with silane fragments and the transition temperature is thought to be pressure dependent. Conditions for the deposition of device quality epitaxial silicon at low temperatures are defined and discussed. Plasma enhancement of the VLPCVD process is discussed in a companion paper. © 1989, The Electrochemical Society, Inc. All rights reserved.