A method of manufacturing a semiconductor device includes forming an isolation pattern on a substrate to define active patterns each having a first contact region at a center portion thereof and second and third contact regions at edge portions thereof. The method further includes forming a buried gate structure at upper portions of the isolation pattern and the active patterns, forming a first insulation layer on the isolation pattern and the active patterns, and etching a portion of the first insulation layer and an upper portion of the first contact region to form a preliminary opening exposing the first contact region. The method still further includes etching the isolation pattern to form an opening, forming an insulation pattern on a sidewall of the opening, and forming a wiring structure contacting the first contact region in the opening.