A phase changeable memory cell array region includes a lower interlayer insulating layer disposed on a semiconductor substrate. The region also includes a plurality of conductive plugs disposed through the lower interlayer insulating layer. The region also includes a phase changeable material pattern operably disposed on the lower interlayer insulating layer, the phase changeable pattern covering at least two of the plurality of conductive plugs, wherein the phase changeable material pattern includes a plurality of first regions in contact with one or more of the plurality of conductive plugs and at least one second region interposed between the plurality of the first regions, wherein the at least one second region has a lower thermal conductivity than the plurality of first regions. The phase changeable memory cell array region also includes an upper interlayer insulating layer covering at least one of the phase changeable material pattern and the lower interlayer insulating layer. The region also includes conductive patterns disposed through the upper interlayer insulating layer and electrically connected to a plurality of predetermined regions of the plurality of first regions.