A semiconductor device includes a first substrate; devices on the first substrate; a second substrate on the devices; gate electrodes stacked on the second substrate and spaced apart from each other in a first direction; channel structures penetrating the gate electrodes, extending in the first direction, and including a channel layer; isolation regions penetrating the gate electrodes and extending in a second direction; a through contact plug penetrating the second substrate, extending in the first direction, and electrically connecting the gate electrodes to the devices; a barrier structure spaced apart from the through contact plug and surrounding the through contact plug; and a support structure on the gate electrodes and including support patterns, wherein the support structure has first through regions spaced apart from each other in the second direction on the isolation regions and a second through region in contact with an upper surface of the barrier structure.