Nuclear resonance profiling was used to measure the distributions of hydrogen incorporated into dry SiO2films by thermal treatments in steam. Thermal oxides were grown on silicon to a thickness of 260 nm in dry O2and were subsequently treated in steam at temperatures of 320 and 500 C for periods lasting between 390 and 6×105s. The concentrations of hydrogen carried in by permeating water were then profiled with 6.4 MeV15N ions using the resonant nuclear reaction1H(15N, &agr;&ggr;)12C. Water was seen to penetrate the films rapidly and to slowly react with the SiO2uniformly throughout the films. Two distinct stages were observed in the buildup of H, indicating that the water/SiO2reaction involves at least two concurrent processes rather than a single‐stage process.