A semiconductor device includes a trench isolation region provided on a substrate and defining first and second active regions separated from each other. A first semiconductor pillar protruding upward from the first active region is provided. A second semiconductor pillar protruding upward from the second active region is provided. A first gate mask extending to cross over the first and second active regions is provided. The first gate mask surrounds upper sidewalls of the first and second semiconductor pillars. A first gate line formed below the first gate mask, separated from the first and second active regions, and surrounding parts of sidewalls of the first and second semiconductor pillars is provided.