Provided is a method for manufacturing a semiconductor device. In the method, a gate oxide layer, a gate polysilicon layer, and a capping oxide layer are sequentially formed on a semiconductor substrate. A photoresist pattern is formed on the capping oxide layer. The capping oxide layer, gate polysilicon layer, and gate oxide layer are sequentially etched using the photoresist pattern as an etch mask. Ions are then implanted into the semiconductor substrate using the photoresist pattern as a mask. A thermal diffusion process is performed to form source/drain regions. The capping oxide layer is removed, and ions are implanted into the gate polysilicon layer. After metal is deposited on the gate polysilicon layer, a silicide is formed.