In an embodiment, a device includes: a first source/drain region; a second source/drain region; an inter-layer dielectric (ILD) layer over the first source/drain region and the second source/drain region; a first source/drain contact extending through the ILD layer, the first source/drain contact connected to the first source/drain region; a second source/drain contact extending through the ILD layer, the second source/drain contact connected to the second source/drain region; and an isolation feature between the first source/drain contact and the second source/drain contact, the isolation feature including a dielectric liner and a void, the dielectric liner surrounding the void.