Abstract
The theory of the kinetics of the thermal oxidation of silicon is extended after critical examination of the solubility and transport behavior of water in silica. From the solubility data for water in silica reported in the literature, the dissolution appears to be a two‐stage process at temperatures up to 1200°C. In the first stage silanol groups are formed at a relatively slow rate. In the second stage these silanol groups react with water forming hydronium ions 
and silicate ions 
fixed to the silica network. The second stage is relatively fast compared to the first stage. Consistent with this the transport of water appears to occur by the ambipolar diffusion of hydronium 
and hydroxyl ions (OH−). The dissolution and transport of water predict a linear‐parabolic rate law, which differs slightly from the one obtained by Deal and Grove. The catalytic role of water in mixed ambients is explained by a simple interaction between 
and 
formed by the oxidation of Si by 
. An expression for oxide growth accounting for this interaction is derived and properly fits the experimental data reported in the literature. It predicts correctly the linear dependence of the parabolic rate constant and the square root dependence of the linear rate constant on water partial pressure. It predicts also the initial growth regime.