A method of manufacturing a semiconductor device includes forming first and second pattern structures on first and second regions of a substrate, respectively, forming a preparatory first interlayer insulating layer covering the first pattern structure on the first region, forming a preparatory second interlayer insulating layer covering the second pattern structure on the second region, the preparatory second interlayer insulating layer including a first colloid, and converting the preparatory first and second interlayer insulating layers into first and second interlayer insulating layers, respectively, by annealing the preparatory first and second interlayer insulating layers.