In this study, Ge₂Sb₂Te₅ and Ge₈Sb₂Te₁₁ were used as an insulator layer to fabricate ReRAM devices. The resistance change is correlated to the appearance or disappearance of a conductivity filament at the surface of the GeSbTe layer. Changes in the electrical properties of ITO/GeSbTe/Ag devices were measured using a I-V-L measurement system. As a result, compared to the ITO/Ge₈Sb₂Te₁₁/Ag device, this ITO/Ge₂Sb₂Te₅/Ag ReRAM device exhibits highly uniform bipolar resistive switching characteristics, such as the operating voltages, and the resistance values.