The growth rate and alloy composition of Si1-xGex layers grown in an industrial chemical vapor deposition (CVD) system have been analyzed as functions of the process parameters at a pressure enabling selective epitaxial growth. We systematically investigate the growth of Si1-xGex with 0.48≪x≪0.8, using GeH4/SiCl2H2 partial pressure ratios up to 1.12, where the GeH4 flow was constant and the SiCl2H2 flow was varied. Epitaxial growth temperatures spanned from 350 to 600 °C. The growth rate and alloy composition were limited by the surface reaction step with an activation energy of 1 eV/mol. A significant growth rate reduction is observed when increasing Si content. This feature is consistent with a passivation of the surface Si bonds with H and Cl atoms typical of chemical vapor deposition Si1-xGex layer growth. It is found empirically that x/(1-x)∝pDCSΔn, Δn=0.32, where x is the Ge mole fraction and pDCS is the SiCl2H2 partial pressure. Then we tentatively de- velop a model to support the empirical laws found without making any assumption on the mechanism and we extend it to the full compositional range of CVD grown Si–Ge alloys.