In this article, we adopted the rapid thermal oxidation (RTO) method to grow gate oxide layers on Si substrates. These RTO oxides were grown in both O-2 atmosphere (dry RTO oxide) and in H-2 and O-2 mixed atmosphere (wet RTO oxide) at above 1000 degreesC. For comparison, conventional furnace oxides were grown in H-2 and O-2 mixed atmosphere (furnace wet oxide) as the contrast samples. In this experiment, wet RTO oxides showed better electric characteristics than dry RTO oxides. We also found that a postannealing in nitric oxide (NO) atmosphere can further improve the electric properties of these wet RTO oxides. From these experimental results, we believe that postannealing in NO atmosphere is an effective method to improve oxide electric characteristics. We also found that wet RTO oxide has a superior ability to resist a constant current stress.