A capacitor of a semiconductor device includes a first insulating layer having a contact hole therethrough and a contact plug that is in the contact hole and electrically connected to a semiconductor substrate. Also, a diffusion barrier layer is on the contact plug and fills the contact hole, and a storage node is on the insulating layer in contact with the diffusion barrier layer. The storage node has a uniform outer surface morphology and a cavity therein. A second insulating layer is on the first insulating layer and separates the storage nodes from adjacent storage nodes, and a fill layer fills the cavities of the storage nodes. A dielectric layer having a large dielectric constant covers the second insulating layer, the fill layer, and the storage nodes, and a plate node is on the dielectric layer. The storage node has a smooth surface adjacent the dielectric layer, which decreases leakage current. The diffusion barrier layer is buried in the contact hole and avoids oxidation that would otherwise increase contact resistance.