Thermal analysis of a segmented thermoelectric generator is performed, and the segmented leg configurations maximizing the efficiency and the output power are formulated. The effect of operating conditions such as external load resistance, the temperatures of hot and cold junctions, on the device performance is studied. The segmented thermoelectric generator has the leg configuration consisting of the combination of modified lead telluride and modified bismuth telluride. The segmented thermoelectric generator performance, such as device efficiency and output power, is compared with those corresponding to a single material leg configuration (modified lead telluride or modified bismuth telluride) for various operating conditions. It is found that a unique value of the segmented leg combination maximizes the efficiency and the output power for each operating condition. The variation in the operating conditions changed the locus points of the maximum efficiency and the maximum output power. The segmented thermoelectric generator gives rise to the higher device efficiency and the output power than those of the single material leg configuration, especially for the low external load resistance. Copyright (C) 2016 John Wiley & Sons, Ltd.