A method for manufacturing a semiconductor device. In one example embodiment of the present invention, a method for manufacturing a semiconductor device includes various steps. First, a gate pattern is formed on a substrate. Next, a first oxide layer is formed on the gate pattern. Then, a second oxide layer, a first silicon nitride layer, and a second silicon nitride layer are sequentially formed over the substrate and the first oxide layer. Next, a first etching process is performed to remove horizontal portions of the first and second silicon nitride layers. Then, source/drain regions are formed in the substrate. Next, the vertical portions first and second silicon nitride layers are removed. Then, a third silicon nitride layer is formed over the second oxide layer. Finally, a second etching process is performed to remove horizontal portions of the third silicon nitride layer and the second oxide layer.