The electrical switching behaviour of CdTexS1-x-doped borosilicate glass was studied by determining the d.c. current-voltage characteristics using a current source. The I-V characteristic is non-linear for high current density, leading to deviation from Ohm’s law. The experimental data have been analysed assuming that the increase in the glass conductivity is dominated by the Joule effect. The theoretical model used is in good agreement with the experimental results.