X-ray diffraction and differential scanning calorimetric studies were performed on bulk Sn–Sb–Se chalcogenide alloys, which were obtained by the conventional melt quenching technique. The addition of Sn reduces the crystalline nature of Sb 20 Se 80 chalcogenide alloy and amorphous samples are obtained for a-Sn x Sb 20 Se 80− x 8⩽ x⩽ 18. The T g and T x increase with composition up to the chemical threshold with a sharp change in slope at x= 10, corresponding to the average coordination number Z= 2.40, where a Philip–Thorpe rigidity transition occurs. Thin films were obtained by the thermal evaporation method for dc conductivity and optical measurements. From the temperature dependence of dc conductivity measurements, the activation energy (ΔE) and the pre-exponential factor (σ 0) were calculated for each glassy alloy. An approximate linear dependence of ln σ 0 on ΔE is observed which proved the validity of the Meyer–Neldel rule in the investigated samples. It has been observed that the difference in dc activation energy (ΔE) is less than half of the optical band gap (E 0) indicating that the Fermi level is not located near the centre of the gap.