This invention is embodied in an improved process for growing high-quality silicon dioxide layers on silicon by subjecting it to a gaseous mixture of nitrous oxide (N.sub.2O) and ozone (O.sub.3). The presence of O.sub.3 in the oxidizing ambiance greatly enhances the oxidation rate compared to an ambiance in which N.sub.2O is the only oxidizing agent. In addition to enhancing the oxidation rate of silicon, it is hypothesized that the presence of O.sub.3 interferes with the growth of a thin silicon oxynitride layer near the interface of the silicon dioxide layer and the unreacted silicon surface which makes oxidation in the presence of N.sub.2O alone virtually self-limiting. The presence of O.sub.3 in the oxidizing ambiance does not impair oxide reliability, as is the case when silicon is oxidized with N.sub.2O in the presence of a strong, fluorine-containing oxidizing agent such as NF.sub.3 or SF.sub.6.