Systems and methods for power generation for an aircraft are provided. In one example embodiment, a power generation system for an aircraft includes a thermionic generator arranged to receive heat from at least one heat source. The thermionic generator is configured to generate electrical power for one or more aircraft systems based at least in part on the heat received from the at least one heat source. The power generation system further includes a thermoelectric generator arranged to receive waste heat from the thermionic generator. The thermoelectric generator is configured to generate electrical power for one or more aircraft systems based at least in part on the waste heat received from the thermionic generator.