In this work, SONOS NAND flash memory with gate-all.around(GAA) and planar structures are investigated using TCAD simulations. According to Gauss’ law, GAA structure has superior program efficiency compared to planar structure. The result shows that 627 electrons are injected in GAA structure, while only 195 electrons are trapped in planar structure. Moreover, for the same reason, pass disturb is also released in the GAA structure.