DopplerS‐parameter measurements have been performed on low‐pressure chemical vapor deposited (LPCVD) Si3N4samples. Annealing of the samples at 1000 °C for times up to 1 h resulted in a decrease of both theSparameter and the positron diffusion length of the silicon nitride. The diffusion length recovers after reimplantation of deuterium, but theSparameter remains low. The data are discussed using a model also applied to understand some electrical properties of the LPCVD nitride.