A method of forming a semiconductor device includes forming line patterns on a substrate, the line patterns defining narrow and wide gap regions, forming spacer patterns in the narrow and wide gap regions on sidewalls of the line patterns, spacer patterns in the wide gap regions exposing an upper surface of the substrate, and spacer patterns in the narrow gap regions contacting each other to fill the narrow gap regions, forming an insulating interlayer to cover the spacer patterns and the line patterns, forming at least one opening through the insulating interlayer, the opening including at least one contact hole selectively exposing the upper surface of the substrate in the wide gap region, the contact hole being formed by using the spacer patterns in the narrow gap region as an etching mask, and forming a conductive pattern to fill the opening.