A method for manufacturing a semiconductor device is provided. A substrate having a first gate and a second gate respectively formed in a first region and a second region is provided. An underlayer is formed on the substrate to cover the first gate in the first region and the second gate in the second region. A patterned mask with a predetermined thickness is formed on the underlayer in the first region. The underlayer corresponding to the second gate in the second region is removed by the patterned mask to expose the second gate, wherein the underlayer corresponding to the first gate in the first region is partially consumed to expose part of the first gate.