A semiconductor device includes a substrate, a bit line structure on the substrate, a contact plug structure being adjacent to the bit line structure and extending in a vertical direction perpendicular to an upper surface of the substrate, and a capacitor electrically connected to the contact plug structure. The contact plug structure includes a lower contact plug, a metal silicide pattern, and an upper contact plug that are sequentially stacked on the substrate. The metal silicide pattern has an L-shaped cross section.