In this paper, the phase change characteristics of Sb-Te-Se films were systematically studied by in-situ resistance-temperature measurement, X-ray diffraction (XRD), Raman scattering spectroscopy, X-ray photoelectron spectra (XPS), and Transmission electron microscopy (TEM). For preferred Sb56Te24Se20 and Sb55Te22Se23 films, the temperature for 10-year data retention can be up to 93.1 and 102.6°C, which are higher than that of Ge2Sb2Te5 (GST, 82°C). Both amorphous and crystalline resistivities increase with Se content. The resistance ratios between two states maintain almost 4 orders of magnitude. The microstructure of annealed Sb-Te-Se films exhibits uniform distribution of crystallized phases with rhombohedra Sb2SeTe2 and hexagonal Sb. The improvement in thermal stability of Sb-Te-Se films results from the atomic arrangements and consequently the complex cross bond system.