Method for manufacturing flash memory device

A method for manufacturing a flash memory device is capable of controlling a phenomenon in which a length of the channel between a source and a drain is decreased due to undercut. The method includes forming a gate electrode comprising a floating gate, an ONO film and a control gate using a hard mask pattern over a semiconductor substrate, forming a spacer over the sidewall of the gate electrode, forming an low temperature oxide (LTO) film over the entire surface of the semiconductor substrate including the gate electrode and the spacer, etching the LTO film such that a top portion of the source/drain region and a top portion of the gate electrode are exposed, and removing the LTO film present over the sidewall of the gate electrode by wet-etching.