A theoretical model is presented for the anodization of silicon in an oxygen plasma. The model is based on the space‐charge‐limited drift of negative oxygen ions through the growing oxide film to react at the silicon‐silicon dioxide interface. In the initial linear growth region the supply of ions from the plasma determines the growth, whilst for longer periods the drift of ions through the oxide gives rise to parabolic growth kinetics. The theory is consistent with the lack of orientation dependence observed for the plasma oxidation of silicon. It is applicable over the whole of the growth kinetics, for anodization in both constant voltage and constant current modes. The dependence of current and voltage with time during anodization may also be predicted. The theory is shown to be applicable to oxide growth occurring in both an inductively coupled, rf‐stimulated plasma and a microwave‐sustained oxygen plasma over a range of experimental conditions.