Schottky diodes with catalytic metal gates fabricated on SiC are suitable for sensing of hydrogen containing gases. The device performance, including reproducibility and long term stability, is improved by including an ozone treatment in the device processing. In this investigation, the properties of the oxide layer formed on 4H SiC by such ozone treatment are studied with spectroscopic ellipsometry. It was found that both the oxide thickness and its properties are different compared to those for a native oxide formed without ozone treatment.