The thermal contact can influence the output performance of thermoelectric generators. However, in some applications, the heat source cannot afford an enough heating area for thermal contact. Therefore, compact thermoelectric generators based on optimized thermal contact interface should be designed and developed. In this paper, three-dimensional thermal extensional structures are designed, simulated, implemented and tested to optimize the thermal contact interface of compact thermoelectric generators. The result indicates that the compact thermoelectric generators based on three-dimensional thermal extensional structures can reduce the requirement of thermal contact area and make the heat flow directionally transferred to thermoelectric modules along the three-dimensional structure. In only 3600 mm(2) thermal contact area, the compact thermoelectric generators based on the threedimensional structure can generate 5.58 V and 829 mW within 900 s. (C) 2015 Elsevier Ltd. All rights reserved.