The location of implanted arsenic (As) atoms in silicon dioxide (SiO2) matrix is discussed based on avalanche injection experimental results. A model is proposed in which As atoms substitute for Si at two different sites in an oxygen‐deficient SiO2network. With an additional supply of oxygen, but one insufficient to achieve a fully oxidized system, As tends again to occupy Si sites but interstitial As atoms can also be present. In a fully oxidized network As is also oxidized, i.e., As is again incorporated on Si sites. In the frame of this model contradictory results of As diffusion in SiO2obtained by other authors can be understood in a consistent way. ©1995 American Institute of Physics.