A flash includes a substrate comprising an active region and two electron storage structures disposed at two sides of the active region, wherein each of the electron storage structures comprises a silicon oxide/silicon nitride/silicon oxide composite layer. A buried gate is embedded in the active region, wherein the buried gate only consists of a control gate and a gate dielectric layer, and the gate dielectric layer is formed by a single material. Two source/drain doping regions are disposed in the active region at two sides of the buried gate.