Abstract: A semiconductor device includes a PCM stack that includes bottom electrode liner over a lower heater. The bottom electrode liner has a top-down view plus (+) geometry with a ‘horizontal’ portion being orthogonal to a ‘vertical’ portion. An airgap is formed within the PCM stack in an area located adjacent and between the ‘horizontal’ portion and the ‘vertical’ portion. The airgap has a substantially smaller dielectric constant than the surrounding PCM stack material(s). Therefore, the airgap may effectively reduce the amount of current that leaks from the PCM stack when flowing from the bottom electrode liner to a top contact or top electrode. Further, the airgap may allow for expansion of the surrounding PCM stack material(s) that may result from the heating of the PCM stack.