Investigations of the reaction kinetics of the deposition of silica and phosphosilicate glasses were made to determine the parameters governing the rates of reactions. Dependence of deposition rates on substrate temperature shows that the reactions obey the absolute rate theory of heterogeneous reactions at a solid surface. The silane oxidation reaction is of half‐order with respect to oxygen, of half‐order with respect to silane, and of first‐order over‐all. The phosphine oxidation reaction is of second‐order over‐all. The unusual decrease in deposition rate with increasing oxygen concentrations, during the oxidation of silane, has been shown to originate from the adsorption of oxygen on the silicon substrates, retarding the reaction.