The current-voltage (I-V) characteristics of amorphous Ge25BixSb15-xS60 (x = 0, 5, 10 and 15) thin film samples sandwiched between metal electrodes have been investigated as a function of composition, deposition rate (0.61-2.65 nm s(-1)), film thickness (128.6-598.2 nm) and temperature (130-373 K). The current-voltage characteristics are ohmic in the lower field regime followed by non-ohmic behavior in the higher voltage regime, which has been satisfactorily explained by the modified Poole-Frenkel effect. The experimentally determined values of Poole-Frenkel factor (beta(PF)) for different film composition, deposition rate and thicknesses are in good agreement with the theoretically calculated values. Fitting the room temperature data with Jonscher's field-independent re-trapping model is an indication that a modified Poole-Frenkel process is operating. The Hall model can account for the low-temperature dielectric constant, and gives an indication of modified Poole-Frenkel emission. (C) 2002 Elsevier Science B.V. All rights reserved.