The d.c. conductivity of Al-(GeSe5)(1-x)Tl-x-Al thin film samples (0 < x < 20 at.%) has been investigated at high applied electric fields up to 1.10(8) V m(-1) at room temperature. From the current-voltage characteristics, the values of the work function at the Al-GeSeTl interface (X = 0.84 eV), the relative dielectric permittivity of the layers (epsilon = 6.67) and the effective electron mass in the conduction band (m(c)/m = 0.29-1.1) have been determined. The experimental results agree well with the theory of Christov for injected electron currents.