Integrated circuit devices are provide having a vertical diode therein. The devices include an integrated circuit substrate and an insulating layer on the integrated circuit substrate. A contact hole penetrates the insulating layer. A vertical diode is in lower region of the contact hole and a bottom electrode in the contact hole has a bottom surface on a top surface of the vertical diode. The bottom electrode is self-aligned with the vertical diode. A top surface area of the bottom electrode is less than a horizontal section area of the contact hole. Methods of forming the integrated circuit devices and phase change memory cells are also provided.