Abstract: A method comprises forming a first fin including alternating first channel layers and first sacrificial layers and a second fin including alternating second channel layers and second sacrificial layers, forming a capping layer over the first and the second fin, forming a dummy gate stack over the capping layer, forming source/drain (S/D) features in the first and the second fin, removing the dummy gate stack to form a gate trench, removing the first sacrificial layers and the capping layer over the first fin to form first gaps, removing the capping layer over the second fin and portions of the second sacrificial layers to from second gaps, where remaining portions of the second sacrificial layers and the capping layers form a threshold voltage (Vt) modulation layer, and forming a metal gate stack in the gate trench, the first gaps, and the second gaps.