A newly formulated kinetic theory for thermal oxidation of silicon is reviewed. The new theory does not involve the rate-limiting step of the interfacial oxidation reaction, instead it is supposed that the diffusivity is suppressed in a strained oxide region near the SiO2/Si interface. The expression of the parabolic constant is the same as that of the Deal-Grove model, while the linear constant makes a clear distinction with the model. The estimated thickness using the new expression is close to 1 nm, which compares well with the thickness of the structural transition layer. The origin of the deviation from the linear-parabolic relationship observed at initial oxidation stages can be explained by the enhanced diffusion hypothesis, which is opposite conclusion to the Deal-Grove theory.