A semiconductor device includes a substrate including a cell array region and a core region disposed around the cell array region; a plurality of storage element contacts; a contact plug; and a contact plug spacer. The plurality of storage element contacts may include a first storage element contact and at least one second storage element contact, the first storage element contact is a closest storage element contact of the plurality of storage element contacts to the core region, such that the first storage element contact is between the core region and the at least one second storage element contact. A step difference in a vertical direction perpendicular to the substrate between a top surface of the first storage element contact and a top surface of the at least one second storage element contact is 5 nm or less.