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The electrical properties of zinc oxide (ZnO) epitaxial films grown by chemical vapor deposition (CVD) using high-energy H2O generated by H2–O2 reactions on Pt nanoparticles were evaluated. High-energy ZnO precursors formed by the reaction between dimethylzinc gas molecules and H2O molecules were supplied to the substrate surface. The ZnO epitaxial films were grown directly on a-plane sapphire (a-Al2O3) substrates at 773 K without any buffer layer. The electron mobility (μH) at room temperature increased from 30 to 190 cm 2V− 1 s− 1 with increasing film thickness from 100 nm to 2800 nm. The μH increased significantly with decreasing temperature to approximately 100–150 K, but it decreased at temperatures less than 100 K for films thicker than 500 nm. The μH of the ZnO film (189 cm 2V− 1 s− 1) at 290 K increased to 660 cm 2V− 1 s− 1 at 100 K. In contrast, μH hardly changed with temperature for films thinner than 500 nm. According to a two-layer Hall-effect model, the μH and electron concentration of the upper layer were corrected based on the above results, assuming that the degenerate layer had a thickness of 100 nm.