Method for manufacturing semiconductor device

A semiconductor device and a method thereof are provided. An exemplary method according to an embodiment of the invention includes forming a semiconductor fin over a substrate; forming a dielectric layer over the substrate, the dielectric layer including a first portion extending along a sidewall surface of the semiconductor fin and a second portion disposed over the semiconductor fin, the second portion of the dielectric layer having a thickness greater than a thickness of the first portion of the dielectric layer, forming a dummy gate electrode layer over the substrate, the method further includes patterning the dielectric layer and the dummy gate electrode layer to form a dummy gate structure over the channel region of the semiconductor fin, forming a source/drain feature coupled to the channel region of the semiconductor fin and adjacent to the dummy gate structure, and replacing the dummy gate structure with a gate stack. 提供半导体装置及其方法，依据本发明实施例的例示性方法包含在基底上方形成半导体鳍；在基底上方形成介电层，其中介电层包含沿半导体鳍的侧壁表面延伸的第一部分及设置于半导体鳍