Negative Bias Temperature Instability (NBTI) has become one of the most serious reliability problems of metal- oxide-semiconductor field-effect transistors (MOSFETs). The degradation mechanism and model of NBTI are studied in this paper. From the experimental results, the exponential value 0.25-0.5 which represents the relation of NBTI degradation and stress time is obtained. Based on the experimental results and existing model, the reaction-diffusion model with H+ related species generated is deduced, and the exponent 0.5 is obtained. The results suggest that there should be H+ generated in the NBTI degradation. With the real time method, the degradation with an exponent 0.5 appears clearly in drain current shift during the first seconds of stress and then verifies that H+ generated during NBTI stress. Negative Bias Temperature Instability (NBTI) has become one of the most serious reliability problems of metal-oxide-semiconductor field-effect transistors (MOSFETs). The degradation mechanism and model of NBTI are studied in this paper. From the experimental results, the exponential based on the experimental results and existing model, the reaction-diffusion model with H + related species generated is deduced, and the exponent 0.5 is obtained. The results suggest that With the real time method, the degradation with an exponent 0.5 appears clearly in the drain current shift during the first seconds of stress and then verifies that H + generated during NBTI stress.