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Abstract: 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°C was performed on both CeO2/GaN and CeO2/SiC systems while a higher PDA was carried out on CeO2/SiC system at 1150°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 α-Ce2O3 can only be detected by SiC and GaN with CeO2 annealed at 1150 and 1000°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. [Copyright &y& Elsevier]