Electrical and reliability properties of MOS gate oxides prepared by furnace oxidation of Si in an N2O ambient have been studied. The thickness uniformity of N2O oxides is comparable to that of the control oxides grown at the same temperature. Time-zero breakdown tests reveal similar breakdown field distributions for both oxides. Devices with N2O gate oxides are less susceptible to charge trapping, interface state generation, and transconductance degradation under electrical stressing than devices with gate oxides grown in O2. Significant improvement in time-to-breakdown (tBD) and charge-to-breakdown (QBD) under substrate electron injection was observed for N2O oxides. Under gate injection, the QBD and tBD values of both N2O and control oxides are comparable. This stress polarity dependence is explained by the nitrogen pile-up at the SiO2/substrate interface.