High efficiency segmented thermoelectric unicouples (STUs) made of n-type Bi2Te3 and CoSb3 based alloys and p-type Bi2Te3 and CeFe4Sb12 based alloys have recently been developed at the Jet Propulsion Laboratory (JPL). A 1-D analytical model of STUs, which assumes zero side heat losses, is developed and its predictions are compared with some results of experiments performed at JPL to measure the performance parameters of two STUs, uni8 and uni12. Calculations of the effects of contact resistance and side heat losses on the performance of these STUs are presented and discussed. The results indicate that had 2 uni8 and uni12 been well insulated and the contact resistance per leg similar to50 muOmega cm(2), they could have achieved a conversion efficiency of similar to12%, in the tests performed at T-c = 305-316 K and T-h = 872-885 K. However, the actual contact resistances of similar to146 and 690 muOmega cm(2) per leg and the side heat losses of 3.7 and 1.83 W, for uni8 and uni12, respectively, limited the peak conversion efficiency in the tests to -5.5% and 4.6%, respectively. Calculations indicated that STUs having a total contact resistance similar to50 muOmega cm(2) per leg and being well insulated on the sides could potentially achieve a peak conversion efficiency of 15% when operated between 973 and 300 K.