The native oxidation of As-implanted Si surfaces used in actual ultralarge scale integrated processes are investigated. Quantitative analysis of oxidation is made possible by x-ray photoelectron spectroscopy spectral decomposition of Si 2p into Si4+, Si-x+, and Si0+, and by calculation of SiO2 and SiO, thicknesses using the decomposition results. Here, the sensitivity is such that less than 1 Angstrom change is detectable. The native oxidation of As-implanted (1x10(15)-1x10(16)/cm(2), at 25 kV) Si(100) is compared to that of Si(100) without implantation. The results show that the oxidation rate of As-implanted Si is faster than that of Si without implantation, that the native oxide on As-implanted Si includes more suboxide than that on Si without implantation, and that As is oxidized in deeper regions than Si. These results indicate that As implantation changes the Si native oxidation mechanism itself. We propose an oxidation model of As-implanted to explain our observations, and discuss the validity of this model.