The semiconductor device may include an insulating interlayer on the substrate, the substrate including a contact region at an upper portion thereof, a main contact plug penetrating through the insulating interlayer and contacting the contact region, the main contact plug having a pillar shape and including a first barrier pattern and a first metal pattern, and an extension pattern surrounding on an upper sidewall of the main contact plug, the extension pattern including a barrier material. In the semiconductor device, an alignment margin between the contact structure and an upper wiring thereon may increase. Also, a short failure between the contact structure and the gate electrode may be reduced.