NOVELTY - A self-powered microthermionic converter comprises emitter electrode (33), collector electrode separated from the emitter electrode a micron-scale interelectrode gap (76), self-powered thermal power source in thermal contact with the emitter electrode, mechanism for removing electrons emitted through the emitter electrode, and mechanism for returning the emitted electrons to the collector electrode. The interelectrode gap is less than 10mum.    USE - The invention is for converting heat to electrical energy using thermionic electron emission (claimed). It can be directly incorporated into the chip and other devices, such as micro electro mechanical systems (MEMS), integrated MEMS, and micro fuel cell devices.    ADVANTAGE - The invention provides high-energy conversion efficiencies. It has a small size and relatively long lifetime. It increases the mobility and decreases the necessary size of the converter in combination with the heat source.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are also included for:    (A) a method of converting heat to electrical energy using thermionic electron emission comprising providing an incorporated thermal power source that is in thermal contact with an emitter electrode, heating the emitter electrode with the incorporated thermal power source to cause electrons to be emitted from the emitter electrode, streaming electrons emitted from the emitter electrode across a micron-spaced interelectrode gap to a collector electrode, collecting the electrons reaching the collector electrode, providing the collected electrons to an external electrical load, and returning the electrons to the emitter electrode to complete an electrical circuit; and    (B) a method of manufacturing a self-powered microthermionic converter comprising providing a thermally and electrically insulating material as a substrate, forming fuel cup(s) having outer surface from the substrate through micromachining techniques, depositing thermionic electron emissive layer(s) on the outer surface of the fuel cup to provide an emitter electrode, forming a collector electrode through depositing layer of a thermionic electron emissive material on the substrate while maintaining a micron-spaced interelectrode gap between collector and emitter electrodes, and placing a thermal power source inside the fuel cup.    DESCRIPTION OF DRAWING(S) - The figure schematically illustrates a completely assembled self-powered microthermionic convertor.    Electrical trace (9)    Emitter electrode (33)    Gas collection chamber (70)    Electrical contact wire (74)    Micron-scale interelectrode gap (76)