We utilize a combination of MOSFET- gate controlled diode DC-IV measurements and a very sensitive electrically-detected electron spin resonance technique called spindependent recombination to observe and identify defect centers generated during NBTI in fully processed SiO2 and plasma nttrided oxide (PNO)-based pMOSFETs. In SIO2 devices, we observe the NBTI-induced generation of two Si/SiO2 interface silicon dangling bond centers (Pb0 and Pb1) and very likely an oxide silicon dangling bond center (E'). Our observations indicate that both P b0 and Pb1 defects play major roles in these SiO 2-based devices and also suggest that E' centers could play an important role. In PNO devices, we observed the NBTI-induced generation of a new defect center which is fundamentally different from the Pb0P b1 defects generated durine NBTI in SiO2 devices. Our results indicate that it plays a dominating role in NBTI-induced interface state generation in thin PNO devices and also exhibits a post-negative bias temperature stress (NBTS) recovery. Although we observe different interface state defects, we observed essentially equivalent activation energies in both the SiO2 and PNO devices.