The effect of instantaneous heat treatment (of short duration similar to 60 s) is studied for thermally evaporated Sb2Se3 films using chemical compositional, structural and optical analyses. The results show an amorphous to crystalline phase change at 140 degrees C and a constant composition Sb0.6Se0.4 in the range 150-210 degrees C. These results are compared with those of cw Ar- laser irradiation in an attempt to understand the photo-thermal phase changes induced by laser irradiation. The considerable optical contrast between amorphous and crystalline phases and their stability indicate a good potential for WORM kind of storage applications. However, a good optical contrast between various phases having constant chemical composition in the range 150-210 degrees C hints at the possible reversible phase change kind of storage.