A triode-type field emission device includes an insulating substrate; a cathode formed on the insulating substrate; a field emitter aligned on the cathode, wherein the field emitter includes a plurality of emitter tips and each emitter tip has the diameter of nanometers; an insulating layer positioned around the field emitter for electrically isolating the field emitter; and a gate electrode formed on the insulating layer, wherein the gate electrode is closed to an upper portion of the field emitter. Therefore, the triode-type field emission device may be operable in a low voltage.