The negative-bias temperature instability (NBTI) characteristics of HfN/HfO 2 gated p-MOSFET with equivalent oxide thickness (EOT) of 1.3nm and low pre-existi ng traps are studied. Due to the low pre-existing trap density of HfN/HfO2 ga te stack, the observed NBTI characteristics are intrinsic, rather induced by the fabricating process. The observed characteristics can be compared with those re ported in SiO2 based gate stack and can be explained with the general ized reac tion-diffusion (R-D) model: under negative bias and temperature stressing, holes injected from the Si substrate could cause the Si-H bond breaking at the Si sub strate interface. The H atoms diffuse away into the bulk layer and the Si+ spe cies are left at the interface. The diffusing H atoms and the left Si+ species cause the NBTI characteristics.