Experimental observations are reported concerning the influence of some technological processes on the generation rate of positive oxide charge and interface states during high electric field stress. Our results on positive oxide charge generation are consistent with a model of impact ionization in silicon dioxide and we think that acoustic-phonon runaway is the controlling process for impact ionization in SiO2 in films thicker than 20.0 nm at fields higher than 7 MV/cm. We have found that the positive charge is mainly due to trapped holes when the electrons are injected at the gate/SiO2 interface.