A semiconductor device includes an active region extending on a substrate in a first direction; a device isolation layer on the active region; a source/drain region on the active region; an interlayer insulating layer on the source/drain region; a stopper layer on the interlayer insulating layer; a contact structure passing through the interlayer insulating layer and the stopper layer and electrically connected to the source/drain region; and a conductive through-structure passing through the device isolation layer and the interlayer insulating layer from a lower surface of the substrate, and extending in a third direction, to contact a lower surface of the contact structure and the stopper layer, wherein the stopper layer is in contact with a portion of a side surface of the contact structure, and a lower surface of the stopper layer is lower than an upper surface of the contact structure relative to the substrate.