A semiconductor device includes a substrate having a cell region and a peripheral region, a thyristor on the cell region, a MOS transistor on the peripheral region, and a first silicide layer on the substrate adjacent to the thyristor on the cell region. Preferably, the thyristor includes: a first semiconductor layer, a second semiconductor layer, a third semiconductor layer, and a fourth semiconductor layer on the cell region, vertical dielectric patterns in the first semiconductor layer, the second semiconductor layer, the third semiconductor layer, and the fourth semiconductor layer, and first contact plugs on the fourth semiconductor layer.