Semiconductor device

A semiconductor device may include bit line structures on a substrate, a contact plug structure on the substrate between the bit line structures, and a capacitor electrically connected to the contact plug structure. The contact plug structure may include a first contact plug, a second contact plug, and a third contact plug sequentially stacked. An upper surface of the second contact plug includes an upper recess. The third contact plug may fill the upper recess, and may protrude above the upper recess. An upper surface of the third contact plug may be higher than a top surface of the bit line structures.