The Ga40-xSe60Tex with x = 0.0 and 7 alloys were prepared by quenching technique. The glass transition, crystallization, and melting temperature was determined by differential scanning calorimetry (DSC). The activation energy was calculated for both glass transition temperature and crystallization temperature (E-t and E-c). Thin films were deposited by a thermal evaporation technique with thickness range (30-170) nm. The amorphization could be confirmed by X-ray diffraction and scanning electron microscope (SEM) and the effect of composition and thickness of thin films on the optical band gap values. The mechanism of the optical absorption follows the rule of indirect allowed transition. The energy gap (E-g) increases with increasing thickness, but decreases by adding Te in Ga40Se60. Optical constants measurement such as (refractive index n, the absorption index K and dispersion parameter) has been obtained for films with thickness (170 nm). The real part and imaginary part of dielectric constant are determined. The temperature dependence of conductivity was studied as a function of composition and thickness in the temperature range 288-328 K. It is noticed that activation energy increases as film thickness increases. The obtained results were treated in the frame of chemical bond approach proposed by Blcerano and Ovshinsky [J. Non-Cryst. Solids 74 (1985)] and average coordination number . (C) 2002 Elsevier Science B.V. All rights reserved.