Gate-all-around integrated circuit structures having adjacent island structures are described. For example, an integrated circuit structure includes a semiconductor island on a semiconductor substrate. A first vertical arrangement of horizontal nanowires is above a first fin protruding from the semiconductor substrate. A channel region of the first vertical arrangement of horizontal nanowires is electrically isolated from the fin. A second vertical arrangement of horizontal nanowires is above a second fin protruding from the semiconductor substrate. A channel region of the second vertical arrangement of horizontal nanowires is electrically isolated from the second fin. The semiconductor island is between the first vertical arrangement of horizontal nanowires and the second vertical arrangement of horizontal nanowires.