A semiconductor device includes a substrate, a gate electrode on the substrate and source and drain electrodes disposed at respective sides of the gate electrode. The device further includes a nano-line passing through the gate electrode and extending into the source and drain electrodes and having semiconductor characteristics. The nano-line may include a nano-wire and/or a nano-tube. A gate insulating layer may be interposed between the nano-line and the gate electrode. The source and drain electrodes may be disposed adjacent respective opposite sidewalls of the gate electrode, and the gate insulating layer may be further interposed between the source and drain electrodes and the gate electrode. Fabrication methods for such devices are also described.