It is well known that the figure of merit (ZT) is unreliable in calculating the efficiency (eta) of micro thermoelectric generators system level and unrealistic when comparing the performance of thermoelectric (TE) materials in the same metric units. To solve this problem, we have used COMSOL multiphysics to design a single leg of micro thermoelectric generators model for computing efficiency factors (phi) and internal resistance using TE materials' constants, such as electrical conductivity (sigma), TE conductivity (K), and Seebeck coefficient (alpha). The TE materials were placed between two copper electrodes, and the first data analyzed were the voltages per meter and electric currents per meter. The internal resistances were calculated by taking the ration of voltages to electric currents, and at the same time, the electric powers were calculated from the products of electric currents and voltages yielding power per unit area in mu W cm(-2). The phi were calculated using changes in power (Delta P), temperature gradient (Delta T), and the surface area (A). The obtained results showed that the TE materials with highest 0 when the temperatures are between 375 and 550 K are n -type SiGe and p -type SiGe. When the temperatures are between 550 and 780 K, the TE materials with the highest phi are PhTe-Pbl(2), PhTe-CdTe, and PbTe-SrTe-Na. We noted that the phi obtained from eight TE materials in this work are within the range as those reported in the literature between 0.001 and 0.091 mu W cm(-2) K-2. The TE materials with high internal resistances such as PbS, PhTe, and PbSe have phi that is <0.0001 mu W cm(-2)' K(-)2, and those with low internal resistances have phi in the range between 0.002 and 0.0091 mu W cm(-2) K-2. This work has shown that COMSOL multiphysics is a powerful computational tool that can be used to analyze internal resistances and phi of TE materials in the same temperature ranges. Copyright (C) 2016 John Wiley & Sons, Ltd.