The measurement of d.c. electrical conductivity of the bulk samples of chalcogenide glasses of the system Ge10+xSe40Te50-x (x = 0.0, 13.35, 16.65 at.%) are studied. The activation energies are obtained from conductivity measurements, using Mott and Davis equation. The relationship between the energy of decomposition Ed and composition is discussed in terms of the average heat of atomization. The effect of heat treatment on the structure transformation is investigated by X-ray diffraction and scanning electron microscope.