We consider nitrogen profiling in oxynitrides to be the key technology for next generation Flash Memories, because of its ability to suppress the generation of traps in tunnel oxides. We are trying to develop an oxynitriding technique for tunnel oxides that uses nitric monooxide. This time, we tried to control nitrogen profile in oxynitrides by using reoxidized oxynitride process. By using a three- step oxidationoxynitridation-reoxidation process, we attempted to systematically tune oxidation conditions, to obtain a satisfactory tunnel oxide/Si interface and SILC characteristics. Highly reliable tunnel oxide for flash memory has been achieved using recently developed reoxidized oxynitrides processing, which is characterized by wet oxidationoxynitridation-dry oxidation. This process yields excellent characteristics, such as low oxide trap formation, low leakage current, and high charge to breakdown (Qbd). This three-step oxynitride process is best suited for flash memories having superior Program/Erase (P/E) cycling endurance and data retention characteristics. In addition, I will propose the optimum conditions for the reoxidation process.