Contact and frictional electrification measurements of insulators have been used for a number of years to characterize insulator surface charging. An instrument developed in our laboratory confirms triboelectric series data derived from the conventional field mill technique by measurement of current when a metal plate contacts and then separates from the insulator. In this work we investigated the measurement of this contact-separation current on unbiased gamma (Co-60) irradiated SiO2 thermally grown on single-crystal silicon. To our knowledge, surface charge measurements have not been previously used to characterize irradiated SiO2. Results on wet and dry thermal oxides show that irradiation with total doses of 1 and 2 Mrad (Si) show consistent decrease in contact current. Comparison to flatband voltage shifts indicates that radiation damage of SiO2 grown on Si can be observed with surface charge measurements, although more work is required to determine the potential of this method for quantitative analysis of radiation effects.