The resultant thermoelectric (TE) figure of merit Z, the coefficient of performance (COP), the heat pumping capacity per unit area (Q(c)/S) were derived analytically as functions of I(0), rho(c), kappa(c) and s(c) for a single thermoelement (STE) by taking into account the interface layers, where I(0) is a length of a TE material, rho(c) the electrical interface resistivity, kappa(c) the thermal interface conductivity and s(c) the ratio of the Seebeck coefficient of an interface layer to that of a TE material. As a result, it was first revealed that the increase in Z(0)T of a TE material is not necessarily reflected in the increase in ZT of an STE as long as the interface layers are present. The COP and Q(c)/S are lowered remarkably for s(c) = 0 and kappa(c) <= 10(4) W/m(2) K. However, it was clarified that even for low values of kappa(c), the COP and Q(c)/S return to the original high values (obtained for kappa(c) >= 10(5) W/m(2) K) at s(c) = 0.45 and 0.90, respectively. The definite criterion of s(c) whether or not the boundary Seebeck coefficient has an effect on the enhancement of the cooling performance was indicated quantitatively for an STE with interface layers. (C) 2011 Elsevier Ltd. All rights reserved.