In a conventional nonvolatile memory (NVM), charge is stored in a ploy-silicon floating gate (FG) surrounded by dielectrics. But, it will suffer some limitations for continued scaling of the device structure. Therefore, the nanocrystal nonvolatile memory devices have been investigated to overcome the limit of the conventional floating gate NVM in recently years. Nanocrystal charge storage offers several advantages, the main one being the potential to use thinner tunnel oxide without sacrificing nonvolatility. This is a quite attractive proposition since reducing the tunnel oxide thickness is a key to lowering operating voltage and/or increasing operating speeds. In this thesis, we have fabricated tungsten (W) nanocrystals nonvolatile memory devices. A thin tungsten silicide (W5Si3) layer was deposited on tunnel oxide layer first. The following oxidation was performed in furnace system. The W element tends to segregate downward and precipitate on the tunnel oxide after thermal oxidation. In addition, the silicon element is oxidized into silicon dioxide surrounded tungsten nanocrystals. Also, the carrier gas, such as O2 and N2, were also added as the tungsten silicide deposition. The memory effect and the electrical reliability for W nanocrystals surrounded in different dielectric were also investigated in this study. In addition, the formation mechanism of W nanocrystals with additional silicon oxide capped on tungsten silicide was also investigated. The thicker silicon oxide can effectively control the thermal oxidation condition and prevent thin film degradation. However, the overall oxidation cause the memory window reduction and the electrical characteristics degradation, resulted from the partially oxidation of W nanocrystal to metal-incorporated dielectric. By contrast, we also demonstrated the structure that deposited the charge trapping layer by co-sputtered W and dielectric material as SiO2 or Si3N4 to directly form the W nanocrystal embedded in dielectrics. Besides, the W and Si directly deposited by co-sputtered to adjust the two elements contained ratio had investigated as well in this study. Furthermore, the memory effect and electrical characteristics for germanium (Ge) element incorporated W nanocrystal memory were also discussed. The additional storage element contributes the memory effect. In summary, the memory effect for W nanaocrystal embedded in different dielectric, the effect of the thermal treatment for additional silicon oxide incorporation, and the contribution of the Ge element to the memory effect can be obtained from the fabrication of W nanocrystal memory were finished in this study.