Semiconductor apparatus including a phase change material layer having a first and a second chalcogen layer

Semiconductor unit devices may be arranged between a first insulating layer and a second insulating layer that are apart from each other in a direction normal to a substrate. Each of the semiconductor unit devices may include a selection device layer and a phase change material layer that extend side by side in a direction parallel to the substrate. The phase change material layer may have a superlattice-like structure. The phase change material layer may be arranged along a recess portion that is formed by the first insulating layer, the second insulating layer, and the selection device layer.