A semiconductor device includes a semiconductor device may include, but is not limited to, a semiconductor substrate, an isolation electrode, a gate electrode, a gate insulating film, and a first insulating film. The semiconductor substrate has a first groove and a second groove. An isolation electrode is positioned in the first groove. The gate electrode is positioned in the second groove. The gate insulating film is adjacent to the gate electrode. The first insulating film is adjacent to the isolation electrode. The isolation electrode is greater in threshold voltage than the gate electrode.