Effects of rapid thermal processing (RTP) on 200‐nm‐thick SiO2/GaAs interfaces have been studied with x‐ray photoelectron spectroscopy. RTP has been performed at 910 °C for 9 s with the heating rate of 53 °C/s. Rapid diffusion of Ga through SiO2occurs. The diffusion coefficient of Ga in SiO2for RTP is found to be about two orders of magnitude larger than that for conventional furnace processing. The heating rate dependence of the Ga outdiffusion is also reported in the range 31–83 °C/s. In addition, slight loss of As is observed. These results are discussed on the basis of the RTP‐induced thermal stress between SiO2and GaAs.