Measurements have been carried out on the effect of high electric fields on equilibrium conductivity, steady-state photoconductivity, and carrier drift mobility in films of Ge 15Te 81Sb 2S 2 over a range of temperature from 90 K to 300 K. For each of these properties, the dependence on electric field, ε, is of the form exp(− ebε/ kT), where the factor b depends on the particular property concerned and on temperature. The conductivity returns a value for b which decreases with temperature, while the reverse is true for drift mobility. The value obtained for the photoconductivity depends on the prevailing recombination regime. At both high and low temperature, the photoconductivity is linearly dependent on photon flux, and the field dependence is smallest, while in the intermediate temperature regime, where square-root (bimolecular) behaviour prevails, a value of b is found which is just 1/2 that for the dark conductivity. A consistent model for all of this behaviour is described, which involves extended state transport with multiple-trapping in band-tails, negative-U recombination centres appropriate to chalcogenides, and an electric field-dependent emission prefactor which is necessarily common to all gap-states, i.e., the shallow states controlling the drift mobility, and also the deeper lying recombination centres. Such an effect can arise from field-induced delocalisation of states near the mobility edge.