The location of positive trapped charge in the dry thermally grown films of SiO2 on Si in MOS structures has been investigated by combining the internal photoemission-voltage dependence from both interfaces with the capacitance-voltage technique. Trapped holes have been produced in the SiO 2 by vacuum ultraviolet (vuv) photons, x rays, and high-field stressing. After irradiation under positive gate bias, trapped holes have been found to reside near the Si-SiO2 interface with an upper limit of about 50 Å determined for their centroid from this interface. After irradiation under negative bias, a similar situation was found to occur near the Al-SiO2 interface; and in addition some positive charge was found approximately at the Si-SiO2 interface. After high-field stressing under negative bias, positive charge was found approximately at the Si-SiO 2 interface. The charge locating technique is described in detail as well as the implications of the results to radiation damage and insulator breakdown.