A method of manufacturing a semiconductor device includes forming conductive structures on a substrate. Each of the conductive structures has a line shape that extends along a first direction parallel to the substrate. Insulating spacers are formed on upper sidewalls of the conductive structures. An insulating interlayer is formed that covers the conductive structures. A portion of the insulating interlayer between the conductive structures is etched to form a contact hole. An upper portion of the contact hole is larger than a lower portion thereof. The upper portion of the contact hole has a first width along the first direction and a second width along a second direction parallel to the substrate and substantially perpendicular to the first direction. The first width is substantially larger than the second width. The contact hole is filled with a conductive material to form a contact plug.