Various ultrathin oxynitride gate dielectrics of similar thickness processed by a rapid thermal NO-nitrided oxide (RTNO), a remote plasma nitrided oxide (RPN), a remote plasma nitridation of oxide with rapid thermal NO annealing , and a rapid thermal reoxidation of remote plasma nitrided oxide (ReoxRPN) are reported for the first time as a means to extend the reliability scaling limit of /oxynitride-based gate dielectrics. The gate dielectric films show superior interface properties, significantly reduced leakage current, and improved reliability compared to other gate dielectrics fabricated by different processes.