A semiconductor device including a first insulating structure on a substrate and including a first etch stop layer and a first interlayer insulating layer on the first etch stop layer, a second insulating structure on the first insulating structure and including a second etch stop layer and a second interlayer insulating layer on the second etch stop layer, a conductive line penetrating through the second insulating structure, and extending in a first direction parallel to an upper surface of the substrate, and a plurality of contacts penetrating through the first insulating structure and connected to the conductive line may be provided. The conductive line may include a protrusion extending below the second insulating structure and penetrating through the first interlayer insulating layer to be in contact with the first etch stop layer.