The formation of germanium nanocrystals embedded in silicon-oxygen-nitride (SiON) layer acting as distributed charge storage elements is proposed in this work. A large memory window is observed due to the isolated Ge nanocrystals in the SiON gate stack layer. The Ge nanocrystals were nucleated after the high-temperature oxidation of SiGeN layer. The nonvolatile memory device with the Ge nanocrystals embedded in SiON stack layer exhibits 4 V threshold voltage shift under 7 V write operation. Also, the sequent high-temperature oxidation of the SiGeN layer acting as the blocking oxide is proposed to enhance the performance of nonvolatile memory devices.