Abstract: Radioisotope thermoelectric generators (RTG) are widely applied in spacecraft for the deep space exploration. In order to enhance the output power and the area-specific power of the thermoelectric modules, Bi₂Te₃-based thermoelectric modules with different thermoelement cross-areas are prepared. An experiment setup is built to measure the output power of the thermoelectric modules as well as the load resistances under conditions of different temperature differences. According to the test results, when the number of p-n junctions is specified, higher thermoelement cross-areas and higher occupancy ratios result in higher output powers and lower matched loads. With a module with a thermoelement cross-area of 1.6 mm×1.6 mm and an occupancy ratio of 0.406, the maximum area-specific power around 0.282 W·cm^-2 is reached when the temperatures of the heat source and the heat sink are 450 K and 300 K, respectively. In ideal and practical cases, the area-specific powers of the modules with occupancy ratio of 1 are analyzed.