The stability of flash-evaporated amorphous Ge2Sb2Te5 thin films has been studied under medium-term temperature treatment (30 - 80 degrees C, with a step of 10 degrees C) in ten subsequent heating and cooling cycles. The significant changes in structure and optical properties are reported. The temperature cycling of the films resulted in formation of an isolated 5 - 7 turn nano-crystalline phase in the amorphous phase. The corresponding increase in refractive index and change in optical bandgap energy and sheet resistance are also presented. The formation of Ge2Sb2Te5 nano-crystals (similar to 5 - 7 nm) even under temperature below 80 degrees C could contribute to the explanation of mechanism of resistivity fluctuation (drift) of the "amorphous phase" films. We also show that the optical and electrical properties of flash evaporated Ge(2)Sb(2)Tes thin films are very similar to those reported for sputtered films. (C) 2009 Elsevier B.V. All rights reserved.