Improved inner spacers for semiconductor devices and methods of forming the same are disclosed. In an embodiment, a semiconductor device includes a substrate; a plurality of semiconductor channel structures over the substrate; a gate structure over the semiconductor channel structures, the gate structure extending between adjacent ones of the semiconductor channel structures; a source/drain region adjacent of the gate structure, the source/drain region contacting the semiconductor channel structures; and an inner spacer interposed between the source/drain region and the gate structure, the inner spacer including a first inner spacer layer contacting the gate structure and the source/drain region, the first inner spacer layer including silicon and nitrogen; and a second inner spacer layer contacting the first inner spacer layer and the source/drain region, the second inner spacer layer including silicon, oxygen, and nitrogen, the second inner spacer layer having a lower dielectric constant than the first inner spacer layer.