One of a way to achieve high power performance of a thermoelectric device is to broaden the operating temperature range of thermoelectric materials. In order to realize this, a project team has carried out cooperative research and they have developed 3-stage segmented thermoelectric elements. The element is composed of three kinds of optimized thermoelectric materials: SiGe; PbTe; and Bi/sub 2/Te/sub 3/. The segmented element can work over a wide range from room temperature to 1073 K. Every stage of the thermoelectric element was prepared both in monolithic and 2 layer-stepwise structures, and they simply called the 3-stage element, constructed by gradient thermoelectric materials, FGM (functionally graded materials). For confirming the effect of large temperature range of the 3-stage segmented element, they also prepared a standard monolithic SiGe element, which was machined the same size as the segmented one. Evaluations for every element included electric resistance, generative current and power output. A large-temperature-span apparatus conducted the performance evaluations, and a high accuracy electronic load was used in this experiment. The results indicate that highest efficiency up to 17% is possible for the 3-stage segmented element, which was constructed by monolithic SiGe, PbTe and Bi/sub 2/Te/sub 3/. Amount of total resistance in the 3-stage segmented element significantly affects the power output. Improvement of the joining process for a stepwise graded element will greatly contribute to high power performance.