The advantages and drawbacks of Capacitance vs Voltage (CV) characteristics, trap-assisted gate leakage tunneling and multi-frequency charge pumping techniques, have been brought out through an attentive investigation of oxide defects in CMOS technologies. To this purpose, the importance of the extension of the accessible regions of the oxide in energy and depth and the influence of model parameters, are discussed using a novel methodology based on a multiphonon charge trapping model. The significant differences found in the probed regions and their localization in the oxide extracted with the three techniques constitutes an important information for process development and oxide quality optimization.