The electrical conduction mechanism contributing to the leakage current at different field regions and different temperatures have been studied in this work. The current-voltage (I-V) measurement of TiN/HfO2/SiO 2/P-Si nMOS capacitor, taken before and after constant voltage stress suggests that Poole-Frenkel mechanism is the dominant conduction mechanism. It was also observed that at low field region Ohmic conduction dominates. Trap energy level (φt) of 0.36 eV, obtained from Poole-Frenkel mechanism indicates that the defect is oxygen-related and is a good match with the reported value for V-/V-- in HfO2. Significant charge trapping at low level stress was observed whereas at high level and elevated temperature stressing suggests a variation of trap energy level indicating new defect formation.