Semiconductor devices having improved electrical characteristics are described, as are methods of fabricating the same. The semiconductor device may include a first gate electrode on a substrate and extending in a first direction, a second gate electrode on the substrate and running across the first gate electrode while extending in a second direction, and a channel structure between the second gate electrode and lateral surfaces in the second direction of the first gate electrode and between the second gate electrode and a top surface of the first gate electrode. The channel structure may include a first dielectric layer that covers in contact with the lateral surfaces and the top surface of the first gate electrode; a second dielectric layer on the first dielectric layer and in contact with the second gate electrode; and a channel layer between the first dielectric layer and the second dielectric layer.