The thermoelectric performance of a material critically depends on whether it can be doped with the desired carrier type (electrons or holes). Furthermore, the carrier concentration of the desired carrier type needs to be tuned to optimize the TE performance. The presence of high concentrations of "killer" chargecompensating native defects can prevent the desired doping. For example, high concentrations of acceptor cation vacancies in Mg 3 Sb 2 and BiCuOSe under cation-poor growth conditions, respectively, prevent n-type doping. In the context of alloy design, it is crucial that the compositions that optimize the electronic and thermal transport are also dopable.