An improved method for fabricating a flash memory on a semiconductor substrate is provided. A patterned gate oxide layer and a patterned mask layer are formed on the substrate. Hard material spacers are formed on sidewalls of the gate oxide layer and the mask layer. A shallow trench isolation is formed in the substrate using the mask layer and the hard material spacers as masks. The hard material spacers and the mask layer are removed. A tunneling oxide layer is formed on a portion of the substrate beside the gate oxide layer. A floating gate is formed over the gate oxide layer and the tunneling oxide layer. A dielectric layer is formed over the floating gate. A control gate is formed over the dielectric layer.