The voltage Delta V and electric current Delta I of the p- and n-type Cu/Bi-Te/Cu composite thermoelectric devices were measured as a function of Delta T for four regions of the intrinsic Bi-Te compound, Cu/Bi-Te and Bi-Te/Cu interfaces and Cu/Bi-Te/Cu composite using thermocouples set at intervals of s = 2 and 6 mm, where the lengths of Bi-Te compound and copper are 4 and 5 mm, respectively. Delta V and Delta I of all regions tended to increase linearly with an increase of Delta T. The resultant alpha was obtained from the relation Delta V/Delta T. The resultant alpha values of regions including the interface are much higher in absolute value than those of the intrinsic Bi-Te compounds, so that the barrier thermo-emf is found to occur in the forward-bias direction. It indicates that the barrier thermo-emf appears even in the semiconductor-metal junction, as in the case of the p-n junctions. The resultant alpha of Cu(T (H))/Bi-Te interface rich in the heat flow increases with an increase of Delta T, while that of Bi-Te/Cu(T-C ) interface poor in the heat flow decreases with an increase of Delta T. The Delta T-dependence of alpha of the interfaces is entirely opposite at the hot and cold sides. As a result, the resultant alpha of the p- and n-type Cu/Bi-Te/Cu composites remained little varied with changes of Delta T, so that the present composites have a thermal stability superior to the intrinsic Bi-Te compounds.The generating powers Delta W (Bi-Te) and Delta W (Cu/Bi-Te/Cu) for the p-and n-type intrinsic Bi-Te compounds and Cu/Bi-Te/Cu composites increased parabolalically with an increase of Delta T, and the ratios of Delta W (Cu/Bi-Te/Cu) to Delta W (Bi-Te) reached great values of 1.41 and 1.45 for the p- and n-type composites, respectively. It was thus found that the enhancement in the resultant alpha of the composite materials results in a significant improvement in the conversion efficiency for generators.