Ga-Sb alloys are potential candidates for phase change random access memory (PCRAM) applications. Ga-Sb alloys of variable compositions including the single stoichiometric GaSb and several Sb-rich compositions were studied using resistivity versus temperature measurements, static laser testing, and time-resolved X-ray diffraction. It was found that the stoichiometric alloy has an unusual inverse optical contrast compared to typical phase change materials as the crystalline phase has lower reflectance compared to the amorphous phase. Sb-rich alloys show a decrease in reflectance upon crystallization at lower temperature but an increase in reflectance at higher temperature from subsequent Sb segregation. Alloys very rich in Sb only show a positive change in reflectance upon crystallization typical for conventional phase change materials. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.