A method of the present disclosure includes forming a fin-shaped structure including a plurality of semiconductor layers, a first hard mask layer, a second hard mask layer, and a third hard mask layer, forming a patterned masking layer having a mask portion and a window portion, wherein the third hard mask layer is exposed through the window portion, performing a first etch process to expose the second hard mask layer through the window portion, performing a second etch process to etch the exposed second hard mask layer and to leave behind second hard mask layer residues, performing a third etch process to remove the second hard mask layer residues, etching the plurality of semiconductor layers in the fin-shaped structure through the window portion to divide the fin-shaped structure into a first segment and a second segment, and forming an isolation feature around the first segment and the second segment.