Taking the actual operating condition of complementary metal oxide semiconductor (CMOS) circuit into account,conventional direct current (DC) stress study on negative bias temperature instability (NBTI) neglects the detrapping of field effect transistors (MOSFETs) inverter operation. In this paper we have studied the degradation and recovery of NBTI under alteating stress, and presented a possible recovery mechanism. The three stages of recovery mechanism under positive bias are fast recovery, slow recovery and recovery saturation.