The discharge behaviour of m.n.o.s. structures with no applied voltage is investigated at temperatures from −155° C to 120° C for times from 10 to 104s. The decay rate is practically independent of the temperature up to 80° C but increases significantly at 120° C. The discharge curves are explained by direct tunnelling from traps, combined with the thermal excitation of these traps. The time dependence of the charge centroid is ascribed to a redistribution of the stored charge in the nitride. A correlation between the decay rate increase after write-erase cycling with the increased nitride conductivity is found.