A semiconductor device including an interlayer insulating layer on a substrate; a conductive line on the interlayer insulating layer; and a contact plug penetrating the interlayer insulating layer, the contact plug being connected to the conductive line, wherein the contact plug includes an upper pattern penetrating an upper region of the interlayer insulating layer, the upper pattern protruding upwardly from a top surface of the interlayer insulating layer, the upper pattern includes a first portion penetrating the upper region of the interlayer insulating layer; and a second portion protruding upwardly from the top surface of the interlayer insulating layer, and a width of a lower region of the second portion in a direction parallel to a top surface of the substrate is greater than a width of an upper region of the second portion in the direction parallel to the top surface of the substrate.