Electrical characterization of SiO2/n-type GaN planar metal-insulator-semiconductor (MIS) capacitors fabricated on sapphire substrates was carried out with a capacitance-time (C-t) technique, C-t measurements after applying strong reversed voltages showed capacitance transients, corresponding to the generation of minority carriers in the MIS structure. This result indicates the formation of inversion mode at the SiO2/GaN interface in the deep depletion state. From the temperature dependence of the capacitance transient, thermal activation energy for the generation of minority hole carriers is estimated to be similar to0.46 eV, which is Much smaller than the GaN band gap. This implies that the observed inversion behavior originates in defects inside the GaN layer. (C) 2002 Elsevier Science Ltd. All rights reserved.