A nonvolatile memory device with nitrided Si nanocrystals embedded in a floating gate was fabricated. The uniform Si nanocrystals with high density (3×10¹¹ cm^-2) were deposited on ultra-thin tunnel oxide layer (~ 3 nm) and followed by a nitridation treatment in ammonia to form a thin silicon nitride layer on the surface of nanocrystals. A memory window of 2.4 V was obtained and it would be larger than 1.3 V after ten years from the extrapolated retention data. The results can be explained by the nitrogen passivation of the surface traps of Si nanocrystals, which slows the charge loss rate.