The depth profile analysis, based on the measurement of high-frequency capacitance-voltage characteristics of an electrolyte-insulator-semiconductor system in the course of the layer-by-layer insulator removal by etching, showed that the formation of a SIMOX structure is accompanied by the appearance of positively charged defects in the oxide layer at the oxide-silicon interface. A change in the charge state of the SIMOX structures under the action of an applied electric field, near ultraviolet (UV) radiation, and low-temperature annealing was studied.