A model has been developed for the chemical vapor deposition of epitaxial Si_1-xGe_x films from SiH₄ and GeH₄. The model is based on a simplified chemical mechanism including adsorption and decomposition of SiH₄, GeH₄ and H₂ on vacant Si or Ge sites and subsequent H₂ desorption. The model focuses on effects at relatively high pressures (i.e. 1-200 Torr) where suppression of deposition by adsorbed hydrogen becomes important, resulting in an inverse dependence of the deposition rate on pressure. In addition as the pressure is increased the Ge concentration of the film is observed to become strongly dependent on temperature. The model assumes that this temperature dependence is due to the influence of adsorbed hydrogen on segregation of Ge to the surface and the relative concentration of vacant Si and Ge sites. The model predictions of deposition rate and Ge concentration compare favorably with experimental data over a wide range of conditions.