The kinetics of the deposition of polycrystalline silicon from silane were studied at 25–125 Pa and 863–963 K using a continuous flow perfectly mixed reactor equipped with a microbalance and a quadrupole mass spectrometer for in situ deposition rate measurements and on-line gas-phase analysis. It was possible to obtain rate coefficients that are intrinsic, i.e., only determined by chemical phenomena. A four-step elementary gas-phase reaction network coupled to a ten-step elementary surface network was able to describe the experimental data. Pressure falloff behavior of gas-phase reactions was taken into account using the Rice-Rarnsberger-Kassel-Marcus theory. In the surface reaction mechanism, adsorption of silane, hydrogen, and highly reactive gas-phase intermediates and first-order desorption of hydrogen are the only kinetically significant steps. Silylene and disilane are the most abundant gas-phase intermediates, causing typically one fifth of the overall silicon growth.