2-bits/cell operation characteristics of WSG-SONOS memory has been fully studied in different ONO thickness. The 2-bits/cell characteristics of WSG-SONOS memory will be determined by tunneling oxide and total ONO thicknesses. Besides, thicker top oxide thickness will contribute to better gate disturbance performance while maintaining the same drain disturbance. We also found that the excellent endurance can be performed for the device with thinner tunneling oxide thickness. Optimized ONO thickness for WSG-SONOS memory will be demonstrated in this paper.