Silicon oxynitride films from the reaction in nitrogen at 850°C are clear, adherent, amorphous dielectrics whose composition may be varied over the entire range between and by controlling the ratio employed. The refractive index is a convenient and accurate measure of the composition. Over much of the nitrogen‐rich range, the Si content is about 2% ower than stoichiometric, and the hypothesis is made that one nitrogen in three is bonded to only two other skeletal atoms instead of three, and that some of these nitrogens bear bonded hydrogen. The N‒H groups are believed to play a role similar to that of O‒H in silicas. Compositions near are highly resistant to ionizing radiation under bias, and are excellent Na+ barriers at 300°C and 106 V/cm. However, they are not better barriers to Na+ thermal diffusion at 600°C than . With appropriate pre‐ and post‐deposition chemical treatments, oxynitride films give low Si surface charge and small nonionicshifts in flatband voltage with bias‐temperature aging. Other properties investigated for various compositions include etch rate, i.r. spectrum, film stress,and cathodoluminescence spectra. Films from the and processes are compared.