Memory device and method of fabricating the same

A memory device comprising:

• a first conductive line extending over a substrate in a first direction;
• a second conductive line extending over the first conductive line in a second direction that intersects the first direction;
• a memory cell pillar interposed between the first conductive line and the second conductive line;
• and
• an insulating wall disposed upright on the substrate, the insulating wall facing a side surface of the memory cell pillar,
• wherein the memory cell pillar comprises:
• a heating electrode layer, which has an L-shaped cross-section and comprises a base portion extending parallel to the first conductive line and a fin portion extending from an end of the base portion in a direction away from the first conductive line;
• and a selection device layer between the first conductive line and the heating electrode layer, and
• a side surface of the selection device layer which faces the insulating wall, and a side surface of the fin portion, which faces the insulating wall, extend along a first straight line.