The authors use a very simple sol-gel spin coating method at 900 degrees C and 1 min rapid thermal annealing to fabricate three different poly-Si-oxide-nitride-oxide-silicon-type flash memories. The memory windows estimated from the curve of drain current versus applied gate voltage are 3, 3.3, and 4 V for (i) HfO2 thin film, (ii) hafnium silicate nanocrystal, and (iii) coexisted hafnium silicate and zirconium silicate nanocrystal memory, respectively. Together with the measurement from gate disturbance and drain disturbance on these fabricated devices, the coexisted nanocrystal devices exhibit better reliability than both the thin film type memory and single nanocrystal type memory. (C) 2007 American Vacuum Society.