A method of fabricating a semiconductor device, in which an interference effect between word lines is substantially reduced or eliminated, includes forming a plurality of gate patterns on a substrate; forming a first insulating layer between the gate patterns, the first insulating layer filling a region between the gate patterns; etching the first insulating layer to remove a portion of the first insulating layer to a predetermined depth; and forming a second insulating layer on the gate patterns and the first insulating layer. A low-dielectric-constant material is formed between the gate patterns.