A method for manufacturing a semiconductor device is disclosed. The method comprises: forming a T-shape dummy gate structure on the substrate; removing the T-shape dummy gate structure and retaining a T-shape gate trench; forming a T-shape metal gate structure by filling a metal layer in the T-shape gate trench. According to the semiconductor device manufacturing method disclosed in the present application, the overhang phenomenon and the formation of voids are avoided in the subsequent metal gate filling process by forming a T-shape dummy gate and a T-shape gate trench, and the device performance is improved.