Chemical composition and growth kinetics of ultrathin SiO2 films formed by rapid thermal oxidizing Si substrates in N2O have been studied. Both Auger electron spectroscopy (AES) and x-ray photoelectron spectroscopy (XPS) revealed nitrogen pile-up at the SiO2/Si interface. Nitrogen concentration at the oxide surface and throughout the bulk was found to be low, similar to reoxidized/nitrided oxides. The nitrogen 1s electron binding energy determined by XPS in the oxide also indicated that these nitrogen atoms were bonded to Si. Electrical characterization showed that N2O oxides exhibited less interface state generation under hot-electron stressing as compared with the control oxide. Growth kinetics study showed that after an initial stage of fast growth, the oxidation rate was reduced significantly due to the formation of a nitrogen-rich layer at the Si/SiO2 interface which blocked oxidant diffusion to the interface.