Results on the thermal analysis, switching characteristics and effect of heat treatment on the structure and electrical resistivity of the chalcogenide glass As25Si45Te30 are reported and discussed. From the dependence of the crystallization peak temperatures, Tp, on the heating rate, the crystallization activation energies were evaluated. For the investigated composition, the most probable mechanisms for the two crystallization phases are three- and one-dimensional crystal growth. Transformation from the glassy structure to the crystalline phase was responsible for the decrease in room-temperature resistivity and activation energy for conduction with increase of the annealing temperature