We report on new photoconductivity fatigue effects and generation of positive fixed charges when nitrogen-rich gate-quality silicon nitride films are illuminated by sub-bandgap ultra-violet light. The photoconductivity fatigue is correlated with the density of neutral silicon dangling bonds measured by electron spin resonance. Spins and positive fixed charges are generated at the same time, but at different rates and in different amounts. Photon energy threshold for spins and positive fixed charges creation is around 3.4 eV. Annealing studies have also shown that a temperature of at least 350°C, and 400°C is needed to fully recover the initial (dark) spins and positive fixed charges densities, respectively, in the film deposited at 400°C. © 1989.