Thermodynamic analysis is presented in terms of dimensionless operating parameters, which includes temperature and load resistance ratios, and dimensionless device pin length for a skutterudite thermoelectric generator. To obtain the device geometric configuration maximising the thermal efficiency, the device characteristics are computed for various values of operating and pin geometric parameters. It is found that the device maximum efficiency does not coincide with the optimum dimensionless device pin length corresponding to the maximum thermal efficiency. Altering load resistance from its optimum value lowers the thermal efficiency considerably and the thermal efficiency variation becomes gradual for the reduced external load resistance. In addition, electrical resistance of the thermoelectric generator beyond its optimum value has an adverse effect on the thermal efficiency.