In this paper, furnace nitridation of thermal SiO2 in pure N2O ambient for MOS gate dielectric application is presented. N2O-nitrided thermal SiO2 shows much tighter distribution in time-dependent dielectric breakdown (TDDB) characteristics than thermal oxide. MOSFET's with gate dielectric prepared by this method show improved initial performance and enhanced device reliability compared to those with thermal gate oxide. These improvements are attributed to the incorporation of a small amount of nitrogen (approximately 1.5 at .%) at the Si/SiO2 interface without introducing H-related species during N2O nitridation.