Methods of forming self-aligned nanowire spacer structures are described. An embodiment includes forming a channel structure comprising a first nanowire and a second nanowire. Source/drain structures are formed adjacent the channel structure, wherein a liner material is disposed on at least a portion of the sidewalls of the source/drain structures. A nanowire spacer structure is formed between the first and second nanowires, wherein the nanowire spacer comprises an oxidized portion of the liner.