In a phase-change semiconductor device and methods of manufacturing the same, an example method may include forming a metal layer pattern on a substrate, the metal layer pattern including an opening that exposes a portion of the substrate, forming an etch stop layer on the metal layer pattern, a sidewall of the opening and the exposed portion of the substrate, the etch stop layer formed with a thickness less than an upper thickness threshold, and reducing at least a portion of the etch stop layer, the reduced portion of the etch stop layer forming an electrical connection with the substrate.