In a method of manufacturing a phase change memory device, an insulating interlayer having a through opening is formed on a substrate, at least one conformal phase change material layer pattern is formed along the sides of the opening, and a plug-like phase change material pattern having a composition different from that of each conformal phase change material layer pattern is formed on the at least one conformal phase change material layer pattern as occupying a remaining portion of the opening. Energy is applied to the phase change material layer patterns to form a mixed phase change material layer pattern including elements from the conformal and plug-like phase change material layer patterns.