A method according to the present disclosure includes depositing, over a substrate, a stack including channel layers interleaved by sacrificial layers, forming a first fin structure and a second fin in a first area and a second area of the substrate, depositing a first dummy gate stack over the first fin structure and a second dummy gate stack over the second fin structure, recessing source/drain regions of the first fin structure and second fin structure to form first source/drain trenches and second source/drain trenches, selectively and partially etching the sacrificial layers to form first inner spacer recesses and second inner spacer recesses, forming first inner spacer features in the first inner spacer recesses, and forming second inner spacer features in the second inner spacer recesses. A composition of the first inner spacer features is different from a composition of the second inner spacer features.