Combined electrical conductivity and thermoelectric power measurements have been made on Eu3S4at temperatures from 100° to 1000°K. These measurements show that the charge carrier concentration in this temperature range is essentially constant. The activation energy for electrical conduction arises, therefore, from the temperature dependence of the drift mobility, and is interpreted as an energy required for the hopping motion of the electronic charge carriers. An abrupt change in resistivity, characteristic of a transition, occurs at about 175°K. The activation energy for conduction above and below the transition is 0.163±0.004 eV and 0.21±0.01 eV, respectively. The Seebeck coefficient data obtained are interpreted in terms of the contribution of the kinetic energy term and the influence of the high charge carrier density on the concentration of available sites.