A semiconductor device includes a substrate having a cell array region and a peripheral region, lower electrodes disposed on the cell array region, at least one supporter layer contacting the lower electrodes, a dielectric layer covering the lower electrodes and the at least one supporter layer, an upper electrode covering the dielectric layer, an interlayer insulating layer covering an upper surface and a side surface of the upper electrode, a peripheral contact plug passing through the interlayer insulating layer on the peripheral region of the substrate, and a first oxide layer between the upper electrode and the peripheral contact plug. The upper electrode includes at least one protruding region protruding in a lateral direction from the cell array region toward the peripheral region. The first oxide layer is disposed between the at least one protrusion region and the peripheral contact plug.