The utilization of metal-organic decomposed cerium oxide (CeO2) film as a gate oxide spin-coated on n-type GaN and SiC for metal-oxide-semiconductor structure has been investigated. Post-deposition annealing (PDA) in oxygen ambient at 1000 degrees C was performed on both CeO2/GaN and CeO2/SiC systems while a higher PDA was carried out on CeO2/SiC system at 1150 degrees C. The cross-sectional images of scanning transmission electron microscopy (STEM) and elemental line profiles of energy dispersive X-ray verified the formation of interfacial layer (IL) and its compound. It had been perceived from STEM that decomposition of GaN substrate during PDA at 1000 C had led to the crack formation on the surface of GaN and this issue was not confronted by the SiC substrate. From X-ray diffraction analysis all samples revealed CeO2 phase, but additional phase of alpha-Ce2O3 can only be detected by SiC and GaN with CeO2 annealed at 1150 and 1000 degrees C, respectively. The transformation of phase might assist in the formation of IL between CeO2 and the substrate. A detailed comparison on the physical and electrical characteristics of the CeO2 gate deposited on both substrates was systematically presented. (C) 2011 Elsevier B.V. All rights reserved.