Fourier transform infrared attenuated total reflectance technique was used to measure the SiOH and SiH contents in the thermal oxide films grown on Si wafers. It was found that the SiOH groups in the bulk could be eliminated by annealing at 850 °C, whereas SiOH at the Si/SiO2interface could only be removed by annealing at 1000 °C. It was also found that SiOH and SiH groups were generated in the thin oxide film by &ggr;‐ray irradiation. The presence of H or H2in SiO2is necessary to explain the result.