A method for fabricating a non-volatile memory semiconductor device is disclosed. The method includes the steps of providing a substrate; forming a gate pattern on the substrate, wherein the gate pattern comprises a first polysilicon layer on the substrate, an oxide-nitride-oxide (ONO) stack on the first polysilicon layer, and a second polysilicon layer on the ONO stack; forming an oxide layer on the top surface and sidewall of the gate pattern; performing a first etching process to remove part of the oxide layer; and performing a second etching process to completely remove the remaining oxide layer.