Semiconductor device and the manufacturing method thereof are disclosed herein. An exemplary semiconductor device comprises a nanostructure disposed over a substrate, wherein the nanostructure includes a plurality of semiconductor layers separated vertically from each other and a dummy pattern layer including dielectric material disposed over and separated vertically from a top semiconductor layer of the plurality of semiconductor layers. The exemplary semiconductor device also comprises a gate structure disposed over a channel region, wherein the gate structure wraps around each of the plurality of semiconductor layers and the dummy pattern layer of the nanostructure.