Amorphous thin 6lms of Ge20Bi4Se76exhibiting n-type conduction are reported for the first time. As compared to a-Ge20Se80films, the modified films (a-Ge20Bi4Se76) show an increase in room-temperature electrical conductivity by several orders of magnitude, a transition from p-to n-type conduction, a decrease in the optical gap from 1.9 to 1.5 eV and a drastic fall in the electrical activation energy from 0.85 to 0.17eV. The correlation of the electrical and optical data suggests the existence of localized states at the conduction band edge arising from the incorporation of bismuth. The decrease of the activation energy for electrical conduction is much larger than the decrease of one-half the optical gap. This indicates unpinning of the Fermi level with a shift towards the conduction band edge.