We have derived an analytic model describing the interior temperature difference as a function of the load current of a thermoelectric generator (TEG); we have also proposed a method to extract the intrinsic and extrinsic Seebeck coefficients and resistances of TEG using experimental current-voltage curves. The decrement of internal temperature difference is almost linearly depending on load current of the TEG. From the experimental results, using a thermoelectric (TE) module with a thermal conductance of 3.52 W/K and a parasitic thermal conductance of 50 W/K, the effective internal electrical resistance was increased by approximately 5%, but the effective Seebeck coefficient was attenuated by approximately 13%, as compared to the intrinsic parameters. The relationship between the output power reduction factor and limited thermal conductance of TEG packaging was also derived. Approximately 25% of the maximum output power is lost because of the parasitic thermal resistance of the TE module used in the experiment. (c) 2012 Elsevier Ltd. All rights reserved.