Si nanocrystal with a high density of 5.1x10(11) cm(-2) and an average size of 7.2 nm has been achieved on the NH3-nitrided tunnel oxide, and the density is higher than that formed on the untreated tunnel oxide by a factor of 3.2. The higher density obtained by this technique is attributed to the lower activation energy for the Si nanocrystal nucleation growth on the nitrogen-containing surface of the nitrided tunnel oxide. The memory device with such a high nanocrystal density demonstrates a 1.79 V threshold voltage shift by programming at 10 V for 10 ms and a negligible memory window degradation up to 10(6) program/erase cycles. The good charge storage capability is evidenced by an extrapolated 10 year memory window of 0.92 V at 150 degrees C.