Abstract: There is provided a thermionic energy conversion device (10,11) comprising an emitter (cathode) (5); a collector (anode) (6); an electrical insulator (2) separating the emitter (5) and the collector (6); a negatively charged field inducing layer (4, 3) adapted to induce a field, the field inducing layer (4, 3) arranged distal the emitter (5) with the collector (6) there between, wherein in use, the device (10,11) is heated such that electrons are excited to escape from the emitter (5) towards the field inducing layer; and the electrons are repelled by the field towards the collector (6) for collection by the collector (6), thereby causing the collector (6) to raise in potential with respect to the emitter (5).