ABSTRACT:A key challenge for the materials chemist is the development of controllable and straightforward synthetic methodologies that will integrate multiple phases/compositions with scalar designed physical properties. The intent of this review is to give a brief summary of some of the current bulk--scaled approaches that might help guide researchers in the design of optimal hetero--structures in large quantity for the further improvement of thermoelectric conversion efficiency. Examples of two--phase combinations on different length scales will be discussed with a focus on the hot carrier filtering effect that results from the selective scattering of carriers with different energies. Based on this strategy, hetero--structures fabricated by both the bottom--up solution approaches at low temperature and top--down solid--state deposition routes that show promise in improving the thermoelectric figure of merit are highlighted, which may help guide researchers in the design of novel hetero--structures for further improvement.