A;self-aligned gate fabrication technique utilizing silicon-on-insulator technology is developed for the fabrication of large uniform arrays of diamond field emitters with self-aligned gate and sharp tip cathode. A uniform array with millions of gated diamond microemitters was reproducibly achieved. The diamond field emitter array, tested in triode configuration with an external anode, has a low turn-on gate voltage of 26 V. A high emission current of 1 muA per tip was obtained at a gate voltage of approximately 60 V and an anode voltage of 200 V. The ability to modulate emission current at low gate voltage allows more practical usage of a diamond field emitter in vacuum microelectronics.