Ultrathin (58 Å equivalent oxide thickness) stacked Si3N4/SiO2 (NO) films with the bottom oxide prepared by rapid thermal oxidation (RTO) in O2 and the top nitride deposited by rapid thermal processing chemical vapour deposition (RP-CVD) were fabricated and studied. Results show that the charge trapping and leakage current of the stacked films are comparable to those of pure SiO2 and low-field breakdown events are significantly reduced. By scaling down the top nitride thickness the commonly observed flatband voltage instability of MNOS devices was minimised, but the low-defect property was still preserved.