Because of the coupling of the temperature dependence of gas‐phase reaction rate constants with the steep temperature gradient, present in most CVD reactors, a thin chemical reaction boundary layer can be defined in the gas phase just above the susceptor. This boundary layer will be present under all operating conditions, including lower pressures and irrespective of the kinetic regime of the deposition reaction or the existence of flow and temperature boundary layers. Using this chemical boundary layer concept it proves to be possible to derive deposition rate equations not only for the gas‐phase transport limited regime but also for the gas‐phase kinetic regime, or for the case where surface reactions are rate limiting.