A method for manufacturing a semiconductor device includes forming an insulation film including a trench on a substrate, forming a first metal gate film pattern and a second metal gate film pattern in the trench, redepositing a second metal gate film on the first and second metal gate film patterns and the insulation film, and forming a redeposited second metal gate film pattern on the first and second metal gate film patterns by performing a planarization process for removing a portion of the redeposited second metal gate film so as to expose a top surface of the insulation film, and forming a blocking layer pattern on the redeposited second metal gate film pattern by oxidizing an exposed surface of the redeposited second metal gate film pattern.