In this paper, stress-induced leakage current (SILC) is studied in ultrathin (approximately 50 angstrom) gate oxides grown in N2O or O2 ambient, using rapid thermal processing (N2O oxide or control oxide, respectively). MOS capacitors with N2O oxides exhibit much suppressed SILC compared to control oxide for successive ramp-up, constant voltage dc, and ac (bipolar and unipolar) stresses. The mechanism for SILC is discussed and the suppressed SILC in N2O oxide is attributed to the suppressed interface state generation due to the nitrogen incorporation at the Si/SiO2 interface during N2O oxidation.