Tellurium-free antimony-based phase change memory (PCM) alloys have attracted much attention due to their superior attributes such as fast switching speed, wide resistance window, and low drift. However, programming reproducible intermediate states in such PCM materials has been challenging. In this study, bilayer PCM cells comprised of Ga–Sb films with two different compositions separated by a 1-nm-thick AlO _x diffusion barrier layer were fabricated on Si foundry templates with a Ø120-nm TiN heater and TaN top contact. The current–voltage measurements of the cells exhibit two threshold voltages, separating three stable resistance regions. These cells can be controllably switched among three resistance states, that is, the SET (

$\sim 10^{3} \ \Omega)$

, intermediate (

$\sim 10^{4} \ \Omega)$

, and RESET states (

$\sim 5\times 10^{5}\,\,\ \Omega {)}$

. The phase transitions during switching among three resistance states are discussed and correlated with the device resistance profiles. The stability of the AlO _x barrier layer is investigated with transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDS).