We report the effect of the rapid thermal annealing (RTA) of amorphous silicon oxynitride (a‐SiOxNy:H) thin films on the room‐temperature photoluminescence (PL). Samples were prepared by plasma enhanced chemical vapor deposition. The PL intensity increased by one order‐of‐magnitude after annealing for 20 min at 800 °C compared to that of the as‐deposited sample. We have followed the changes in the chemical microstructure of the materials byinsitureal‐time ellipsometry, and suggest that the annealing is characterized by two distinct mechanisms. The first is that hydrogen effusion from clustered hydrogen and/or =N–H bond breaking occurs in the first 5 min resulting in increasing dangling bond density and no increase in the PL intensity. The second occurs after longer annealing times due to local reconstruction of Si–O and Si–N bonds, rather than diffusional rearrangement of the atomic species. This results in a more dense material with a higher refractive index, fewer nonradiative recombination centers, and more efficient PL. A model is presented to describe both the radiative and nonradiative recombination processes. ©1995 American Institute of Physics.