Abstract: Phase change random access memory (PCRAM) is a research hotspot as a new semiconductor memory due to its scalable ability, high density and rapid phase transition superiority. In this paper, Ge₂ Sb₂Te₅ (GST)-based PCRAM devices were fabricated by magnetron sputtering and standard semiconductor process. Through resistance-voltage (R-V) tests with different voltage pulse widths, multi-level storage capacity in GST-based PCRAM devices was found. By utilizing transmission electron microscopy (TEM), the microstructure at different resistance state was investigated. With the decrease of resistance value, The GST material layer begins to crystallize from the bottom electrode and eventually extends to the top electrode. Finally, achieving the phase transition from amorphous to crystalline state. The results show that the multi-resistive states of PCRAM devices are derived from the different volume ratios of crystalline (amorphous) regions.