Multi-gate semiconductor devices and methods for forming thereof including forming air gaps between the gate and the adjacent source/drain features. A first fin element including a plurality of silicon layers is disposed on a substrate, a first gate structure is formed over a channel region of the first fin element. An air gap is formed such that it is disposed on a sidewall of the portion of the first gate structure. An epitaxial source/drain feature abuts the air gap. A portion of the first gate structure may also be disposed between first and second layers of the plurality of silicon layers.