A theoretical investigation on the gate polarity dependence of Fowler-Nordheim (FN) tunneling electron initiated impact ionization probabilities in the bulk silicon dioxide (SiO2) films as well as hole injection from the anode material (n(+) poly-Si gate or silicon substrate) in metal-oxide-silicon devices is presented. Our theoretical results of the gate polarity dependence of the probabilities of various impact ionization processes under constant current FN stress correlate the experimentally observed positive charge generation/trapping and stress-induced trap creation in thick to thin SiO2 films. (C) 2002 Published by Elsevier Science Ltd.