A general kinetic law governing the thermal growth of oxide films is presented. It encompasses the Deal–Grove linear‐parabolic growth law and Blanc’s growth law as two special cases; it extends to more general cases where the interface reaction rate has a power‐law dependence on oxidant pressure, such as observed in the thermal oxidation of silicon, where neither the Deal–Grove nor the Blanc growth law is applicable. The new growth law is required even for oxidation under atmospheric pressure because of the varying oxidant pressure at the Si–SiO2interface. Probable mechanisms for silicon oxidation are suggested.