We present a model for the calculation of homoepitaxial film growth rates during silicon deposition on Si(100)-2×1 from disilane. Central to this model is the use of thermalized gaseous disilane adsorption probabilities that have been determined as a function of gas and surface temperature by convoluting supersonic molecular beam adsorption probability data with a Maxwell–Boltzmann distribution of incident kinetic energies and angles. These calculations show that the primary adsorption pathway over the entire range of conditions investigated is the so-called trapping-mediated mechanism, in which dissociative chemisorption occurs via a physisorbed intermediate. A second adsorption mechanism, direct chemisorption, is activated by translational energy and does in fact contribute somewhat to adsorption, but only at high gas and surface temperatures. Hydrogen coverages and silicon film growth rates are calculated from a simple surface decomposition kinetic model together with a phenomenological thermal desorption model and compare favorably to experimental measurements. Under conditions of high flux or low surface temperature, the growth rate is limited by hydrogen desorption and therefore increases with increasing surface temperature. In the flux-limited or adsorption-limited growth regime, the growth rate is predicted to decrease with increasing surface temperature due to a drop in the adsorption probability, resulting in a maximum in the growth rate for a given set of deposition conditions. © 2001 American Institute of Physics.