To clarify the point defect reaction in silicon wafers under rapid thermal processing (RTP) at more than 1300°C using an oxidation ambient, the vacancy (V) concentration induced in the wafers by RTP was investigated at various oxygen partial pressures. The V concentration was estimated by evaluating the density of oxygen precipitates after thermal treatment. The degree of supersaturation of interstitial silicon (I) was determined using the estimated V concentration, resulting in the equation (CI−CIeq)/CIeq = A(T)(dXO/dt)0.4. Here, (CI−CIeq)/CIeq denotes the supersaturation of I, A(T) denotes a coefficient depending on temperature T, and dXO/dt denotes the growth rate of the oxide film. Furthermore, the same relationship was confirmed for the oxidation-enhanced diffusion (OED) of dopants (900–1150°C) and oxidation-induced stacking fault (OSF) growth (1100–1240°C). As the Arrhenius plots of A(T) for RTP, OED, and OSF can be represented by a single line, it was determined that A(T) = 1.84 × 10−9exp(2.51 eV/kBT) (h/μm)0.4 in the range 900–1350°C.