Physical characterizations of thermally grown oxide on n-type GaN in N2O ambient have been performed. The present study carried out the test at different oxidation temperature (700-1000 degrees C) in order to investigate the effect of oxidation temperature on the thermal oxide. Fourier Transform infrared spectrometer. X-ray diffraction and X-ray photoelectron spectroscopy were employed to identify the oxide layer formed on top of the GaN. Based on the analysis, Ga2O3 and GaON compounds were found on the sample oxidized at 700-900 degrees C. However, at 1000 degrees C, non-stoichiometry GaxOy and/or GaxOyNz compounds were formed. Apart from that, atomic force microscope results indicated that protrusions of grains appeared on the surface after thermal oxidation. The surface roughness of the oxide layer was also found to be increased with temperature. Besides, cross-sectional energy filtered transmission electron microscopy image revealed that the thickness of the oxide layer was increased with oxidation temperature. Remarkably, the activation energy calculated from the Arrhenius plot was found to be 1.65 eV (159.22 kJ mol(-1)). (C) 2012 Elsevier B.V. All rights reserved.