The deposition of silicon (Si) from silane (SiH4) was studied in the silane pressure range from 0.5 to 100 Pa (0.005 to1 mbar) and total pressure range from 10 to 1000 Pa using N2 or He as carrier gases. The two reaction paths, namely,heterogeneous and homogeneous decomposition could be separated by varying the amount of wafer area per unit volume(wafer-distance variation) and the SiH4 partial pressure as well as the total pressure. Rate constants were derived by fittingthe experimental results. The heterogeneous reaction path could be described by only the adsorption rate constants ofreactive species and the desorption rate constant of hydrogen using a Langmuir-Hinshelwood mechanism. Hydrogen andphosphine were found to suppress the deposition rate at low silane pressures. At high silane pressures or high totalpressures the unimolecular decomposition of silane dominates. The unimolecular rate constant was found to be one to twoorders larger than literature values based on RRKM analyses of high pressure rate data. The relative efficiency of SiH4-N2and SiH4-He collisions compared with SiH4-SiH4 collisions in the unimolecular gas-phase decomposition of SiH4 has beeninvestigated. Helium was found to be a weak collider compared to silane and nitrogen.