forming a stack of channel layers and sacrificial layers on a substrate, the channel layers and the sacrificial layers having different material compositions and being alternatingly disposed in a vertical direction;

patterning the stack to form a semiconductor fin;

forming an isolation feature on sidewalls of the semiconductor fin;

recessing the semiconductor fin, thereby forming a source/drain recess, such that a recessed top surface of the semiconductor fin is below a top surface of the isolation feature;

growing a base epitaxial layer from the recessed top surface of the semiconductor fin;

depositing an insulation layer in the source/drain recess, wherein the insulation layer is above the base epitaxial layer and above a bottommost channel layer; and

forming an epitaxial feature in the source/drain recess, wherein the epitaxial feature is above the insulation layer.