A flash memory has a characteristic of no storage data loss (non-volatile) after power failure, and is especially adaptable to fields of mobile communication, computer storage devices, etc. A SONOS flash memory has a structure of Silicon-Oxide-Nitride-Oxide-Silicon (SONOS), in which the ONO comprises one tunneling oxide layer, one silicon nitride layer and one blocking oxide layer. Based on quantum tunneling effect or hot carrier injection effect, charges (electrons or holes) are injected into the silicon nitride layer via the tunneling oxide layer, and captured by charge traps in the silicon nitride layer to change a threshold voltage of a memory cell in the SONOS flash memory, thus realizing data storage. FIG. 1 is a cross-sectional view of a typical SONOS memory cell. As shown in FIG. 1, the structure of the typical SONOS memory cell is that a source 101s and a drain 101d are located at both ends of a substrate 101 respectively and separated by a tunneling oxide layer 103 which is covered by a silicon nitride layer 105, a blocking oxide layer 107 and a gate 101g sequentially, in which the ONO region consisting of the tunneling oxide layer 103, the silicon nitride layer 105 and the blocking oxide layer 107 is a charge storage region. Because the charge storage region is located between the gate 101g and a channel region of an operation region of a transistor, with a continuous scaling down of a size of a semiconductor device, the operation region of the transistor may interfere with the charge storage region, thus causing reduction of a reliability of the device and a data storage lifetime.