A method of fabricating a memory device may include forming a first conductive line extending over a substrate in a first direction, forming a memory cell pillar on the first conductive line, and forming a second conductive line extending over the memory cell pillar in a second direction that intersects the first direction, such that the first and second conductive lines vertically overlap with the memory cell pillar interposed between the first and second conductive lines. The memory cell pillar may include a heating electrode layer and a resistive memory layer. The resistive memory layer may include a wedge memory portion and a body memory portion. The wedge memory portion may contact the heating electrode layer and may have a width that that changes with increasing distance from the heating electrode layer. The body memory portion may be connected to the wedge memory portion.