A method for manufacturing a semiconductor device, comprising: forming a gate trench on a substrate; forming a gate dielectric layer and a metal gate layer thereon in the gate trench; forming a first tungsten (W) layer on a surface of the metal gate layer, and forming a tungsten nitride (WN) blocking layer by injecting nitrogen (N) ions; and filling with W through an atomic layer deposition (ALD) process. The blocking layer prevents ions in the precursors from aggregating on an interface and penetrating into the metal gate layer and the gate dielectric layer. At the same time, adhesion of W is enhanced, a process window of W during planarization is increased, reliability of the device is improved and the gate resistance is further reduced.