The effects of N2and O2atmospheres on arsenic diffusion in silicon from a doped oxide are studied by the backscattering method. The results indicate that the amounts of arsenic atoms diffused in silicon in a N2atmosphere are smaller than those in an O2atmosphere. This is caused by the differences in the properties of the silicon‐doped oxide interface during diffusion; the elemental arsenic is accumulated at the oxide side of the interface during diffusion in N2, whereas arsenic remains in the state of an arsenic oxide during diffusion in O2and is not accumulated.