N-type metal-oxynitride-silicon capacitors were subjected to a negative bias voltage at an elevated temperature. Under this condition, Negative-bias-temperature-instability (NBTI) was evidenced in capacitance-voltage (CV) characteristics with an accompanying decrease, as determined from inversion layer-related (i.e., generation lifetime) deep-level-transient-spectroscopy (DLTS) measurements, in the carrier generation lifetime. An analysis of the dominant defect supplying minority carriers to the inversion layer at the silicon-oxynitride interface revealed a significant change brought about by NBTI. A full recovery of the carrier generation lifetime was observed after several days at zero bias voltage, and room temperature conditions had elapsed following NBTI. Concurrently, a passivation, as inferred from conventional DLTS measurements, of the NBTI-induced trap density occurred at the silicon-oxynitride interface. These relaxation and deactivation phenomena were discussed in the context of a plausible model involving a reaction at the silicon-oxynitride interface between trivalent silicon dangling bond defects and hydrogenous species.