Methods of fabricating a memory unit are provided including forming a plurality of first nanowire structures, each of which includes a first nanowire extending in a first direction parallel to the first substrate and a first electrode layer enclosing the first nanowire, on a first substrate. The first electrode layers are partially removed to form first electrodes beneath the first nanowires. A first insulation layer filling up spaces between structures, each of which includes the first nanowire and the first electrode, is formed on the first substrate. A second electrode layer is formed on the first nanowires and the first insulation layer. A plurality of second nanowires is formed on the second electrode layer, each of which extends in a second direction perpendicular to the first direction. The second electrode layer is partially etched using the second nanowires as an etching mask to form a plurality of second electrodes. Related memory units, methods of fabricating semiconductor devices and semiconductor devices are also provided.