The characteristics of photoelectrochemically (PEC) generated gallium oxide films on n-GaN using an 0.002 M KOH electrolyte are described. The chemical composition of the resistive layers was analyzed by Auger electron spectroscopy. The DC and HF characteristics of Al/Ti/PEC-Ga2O3 (gallium sesquioxide)/GaN structures were studied with current-voltage and capacitance-voltage measurements, respectively. Under reverse bias we found extremely low leakage currents (< 10(-8) Acm(-2) at -15 V) and a very low interface state density: high-temperature operation (up to 166 degreesC tested) motivates the integration of the described dielectric layer forming technique into GaN based device process schemes. Our method may also be employed as gate recess technology.