The effects of oxidation and annealing temperatures on thermally oxidized GaN were investigated. GaN wafers were oxidized at 750 degrees C, 800 degrees C and 850 degrees C, respectively, and the electrical characteristics and interface quality of the resulting metal-oxide-semiconductor capacitors were compared. Among the three samples, the sample oxidized at 800 degrees C presented the best current-voltage characteristics, capacitance-voltage characteristics in accumulation region and smoothest surface morphology because of better thermal stability and quality of oxide grown at this temperature. Moreover, its electrical breakdown field was higher than the other two orders of magnitude. However, if the sample was annealed at a higher temperature of 850 degrees C, the quality of its oxide was significantly degraded due to the sharply increasing decomposition of both oxide and GaN at higher temperature. Lastly, the higher oxidation temperature of 850 degrees C gave the best interface quality. (c) 2006 Elsevier B.V. All rights reserved.