forming a plurality of fin structures extending along a first direction;

forming a dummy fin structure between two adjacent fin structures, wherein the dummy fin structure also extends along the first direction, and wherein forming the dummy fin structure includes forming a high-k dielectric layer over a deformable layer;

recessing portions of each fin structure;

forming source/drain structures over the recessed fin structures; and

deforming the deformable layer of the dummy fin structure to apply either tensile stress or compressive stress on the source/drain structures.