Negative Bias Temperature Instability (NBTI) is studied in Silicon Oxynitride (SiON) p-MOSFETs using a recently developed Ultra-Fast On-The-Fly linear drain current (UF-OTF IDLIN) method. It is shown that both stress and recovery phases of NBTI are strongly influenced by SiON gate insulator process. Gate insulator nitrogen (N) spatial distribution is shown to impact interface trap generation (ΔNIT) and hole trapping (ΔNh) components of overall threshold voltage shift (ΔVT). A simple, self consistent method is proposed to isolate ΔNIT and ΔNh. It is shown that the time dynamics of stress and recovery phases are strongly correlated, at short time governed by trapping and detrapping of holes, and at long time by generation and passivation of interface traps. © The Electrochemical Society.