The Sb–Te–Se ternary system with suitable composition material Sb44Te11Se45 is proposed for its brilliant thermal stability, which was fabricated by doping with Sb2Se3 to Sb2Te. Compared to the traditional Ge2Sb2Te5, Sb44Te11Se45 film exhibits a higher crystallization temperature of 220 °C, a larger active energy of 4.25 eV, along with ultra‐long data retention of 133.8 °C for 10 years, which means a brilliant thermal stability. It was found that Sb2Se3 doping could decrease the grain size, which makes Sb44Te11Se45 material a more stable material for phase‐change memory (PCM) application. For the PCM cell based on Sb44Te11Se45, the resistance ratio between amorphous and crystalline state is up to two orders of magnitude, sufficient for data resolution. From the view‐point of thermal stability, Sb44Te11Se45 composite film will be a potential phase‐change material for high‐temperature storage application.