Abstract: A method for manufacturing a flash device having a trench source line comprises providing a semiconductor substrate. A pad oxide is formed on a substrate, then forming a nitride layer on the pad oxide. The nitride layer and the pad oxide layer are patterned then etching the substrate to form a trench in the substrate. An ion implantation is performed to dope ions into the substrate under the trench to form the trench source line. Next, refilling material is refilled into the trench, followed by performing chemical mechanical polishing to remove a portion of the refilling material to the substrate. A gate dielectric layer, a first doped conductive layer, an inter conductive dielectric layer, a second conductive layer are formed. The first conductive layer, the second conductive layer and the inter conductive dielectric layer are etched to form gate structure. Subsequently, source and drain regions are formed by ion implantation and halo-doped region is formed under the drain regions by ion implantation.