A semiconductor device may include an insulating layer provided in one body on a substrate, a first gate electrode and a second gate electrode disposed on the insulating layer, the first and second gate electrodes extending in a first direction parallel to a top surface of the substrate, a first channel structure penetrating the first gate electrode and the insulating layer so as to be connected to the substrate, a second channel structure penetrating the second gate electrode and the insulating layer so as to be connected to the substrate, and a contact penetrating the insulating layer between the first gate electrode and the second gate electrode. The contact may be connected to a common source region formed in the substrate, and the common source region may have a first conductivity type. Further, the first gate electrode and the second gate electrode may be spaced apart from each other in a second direction at the same level from the substrate, wherein the second direction intersects the first direction and is parallel to the top surface of the substrate.