Semiconductor structures and methods of forming the same are provided. A method according to the present disclosure includes forming a stack of epitaxial layers over a substrate, forming a first fin-like structure and a second fin-like structure from the stack, forming an isolation feature between the first fin-like structure and the second fin-like structure, forming a cladding layer over the first fin-like structure and the second fin-like structure, conformally depositing a first dielectric layer over the cladding layer, depositing a second dielectric layer over the first dielectric layer, planarizing the first dielectric layer and the second dielectric layer until the cladding layer are exposed, performing an etch process to etch the second dielectric layer to form a helmet recess, performing a trimming process to trim the first dielectric layer to widen the helmet recess, and depositing a helmet feature in the widened helmet recess.