The analysis of defect generations in SiO2 and at SiO2/Si interface during positive/negative high electric field stress of commercial n-channel power VDMOSFETs has been given. Some additional experiments containing the gate bias switching have helped in these defects nature investigations. The combined application of midgap subthreshold technique and charge pumping technique have represented very useful tool for the switching trap behavior revealing. The fixed trap density (Delta N-ft) and switching trap density (Delta N-st) in two power VDMOSFET types during Fowler-Nordheim injections have shown different behaviors. (c) 2005 Elsevier Ltd. All rights reserved.