Sem is a former municipality in Vestfold county, Norway. The 102-square-kilometre (39 sq mi) municipality existed from 1838 until its dissolution in 1988. The area is now part of Tønsberg Municipality. The administrative centre was the village of Semsbyen. Other villages in Sem included Barkåker, Eik, Husvik, Husøy, Ringshaug, and Tolvsrød.