The effect of carrier gas on the gate oxide integrity (GOI) of thick gate oxide (400 angstrom) for U-trench metal-oxide-semiconductor field-effect transistors UMOSFETs was investigated. Ar or N-2 were selected as the carrier gases during gate oxidation, and X-ray photoelectron spectroscopy was used to identify the nitrogen depth profile. It was observed that GOI of the 400 angstrom gate oxide grown at 1175 degrees C can be improved by using Ar as the carrier gas instead of N-2 due to the fact that N-2 interacts with the Si surface during high-temperature oxidation. (c) 2005 The Electrochemical Society.