Hole and electron transport in SiO2 films thermally grown on Si are observed by detecting the carrier arrival at the Si with a shallow junction detector. Carrier generation and injection near the Al-SiO2 interface are achieved by uv photons obtained from a Ne discharge. Following charging of an exposed SiO2 surface by negative ions from a corona discharge, we find large amounts of holes near the Si-SiO2 interface with a dependence on substrate crystallographic orientation. The film charges up to an average field of 14.5±0.5 MV/cm. These findings suggest an alternative mechanism to impact ionization for initiation of breakdown in MOS structures.