In an embodiment, a device includes: a source/drain region adjoining a channel region of a substrate; a contact etch stop layer on the source/drain region; a first source/drain contact extending through the contact etch stop layer, the first source/drain contact connected to the source/drain region; a gate structure on the channel region; a gate contact connected to the gate structure; and a contact spacer around the gate contact, where the contact spacer, the gate structure, the contact etch stop layer, and the substrate collectively define a void between the gate structure and the first source/drain contact.