To clarify the correlation between breakdown characteristics and charge generation under high field electrical stress, we have separated the contributions of the charges generated in the oxide bulk and near the Si/SiO2 interface to oxide breakdown. It is found that the density of positive charges generated near the cathode interface increases monotonically with stress time, and that it was independent of stress conditions immediately before breakdown. No correlation between charge generation in the oxide bulk and oxide breakdown has been observed. These results are new experimental evidences which support the model showing that positive charges generated near the cathode interface are responsible for oxide breakdown. © 1997 American Institute of Physics.