The electrical properties of polycrystalline Ge2Sb2Te5 thin films containing both the metastable fcc phase and the stable hcp phase have been studied. The resistivity and its temperature dependence have been modelled using effective medium approximation. By varying the volume fraction of the two phases it is possible to get films with different resistivities and temperature coefficient of resistance, changing without discontinuity from negative (fcc) to positive value (hcp). Mixed phase films with resistivity almost independent of the temperature are obtained at about 4 mΩ cm.