A novel model of degradation phenomena in amorphous silicon nitride films is presented in this paper. We argue that three center Si-H-Si bonds which have negative effective electron correlation energies are dominant deep trapping centers in the investigated films. A new mechanism of hydrogen migration stimulated by the capture of nonequilibrium holes is proposed. The migration of hydrogen results in the deep center concentration decrease and in the creation of local leakage channels. Experimental evidence is presented in support of the proposed model and suggestions are made about how to obtain silicon nitride films with enhanced stability.