The effects of post-oxidation N2O anneal on conventional thermal oxide are studied. The oxide thickness increase resulting from N2O anneal is found to be self-limiting and insensitive to initial oxide thickness, which makes the thickness of the resulting oxide easy to control. The N2O anneal leads to increased resistance against injection-induced interface-state generation and to reduced hole trapping. No further quality improvement is found when the N2O-annealed oxide is subject to an additional reoxidation. This finding confirms that nitrogen incorporation in the absence of hydrogen is responsible for improving the quality of the conventional oxides.