The invention is directed to a method for forming a memory array. The method comprises steps of providing a substrate having a charge trapping structure formed thereon. A patterned material layer is formed over the substrate and the patterned material layer having a plurality of trenches expose a portion of the charge trapping structure. Furthermore, a plurality of conductive spacers are formed on the sidewalls of the trenches of the patterned material layer respectively and a portion of the charge trapping structure at the bottom of the trenches is exposed by the conductive spacers. An insulating layer is formed over the substrate to fill up the trenches of the patterned material layer. Moreover, a planarization process is performed to remove a portion of the insulating layer until a top surface of the patterned material layer and a top surface of each of the conductive spacers are exposed.