Disclosed are semiconductor devices and methods of forming the same. According to the semiconductor device, gate structures are provided to be buried in a substrate and first dopant regions and second dopant regions are provided at both ends of the gate structures. Conductive lines cross the gate structures and are connected to the first dopant regions. Contact structures are respectively provided in contact holes which are provided between the conductive lines and expose the second dopant regions. The contact structures are in contact with the second dopant regions, respectively. Each of the contact structures includes a pad pattern extending along a sidewall of the contact hole.