[en] A preliminary assessment of using thermionic conversion as a topping cycle for fusion reactors is presented. Because of the absence of restrictive temperature limitations for fusion-reactor blankets, fusion reactors may offer significant advantages, compared to fission reactors and fossil-fuel energy sources, for utilizing thermionic topping cycles. A system with a thermionic topping cycle and a conventional steam-turbine generator that utilizes the heat rejected by the thermionic converters is presented for illustration. This system consists of conceptual laser-fusion reactors with high-temperature radiating reactor blankets serving as heat sources for the thermionic topping cycle. The design concept appears to be equally adaptable to magnetically confined fusion reactors. For the example analyzed, net conversion efficiencies of combined thermionic and steam-turbine cycles are high, exceeding 50 percent for some values of the operating parameters, and the cost of producing low-voltage direct current for electrochemical processing is low