Arrays of uniform gated Si field emitters with small gate-tip spacing and sharp tips were fabricated using a newly developed self-aligned process. Emitter tips with 80 nm gate-tip spacing were fabricated and low temperature plasma oxidation was used to sharpen the emitter tips. The enhancement factor of the field emitters increased by a factor of 2.6 after the emitter tips radius was reduced from 67 to 8 nm by plasma oxidation. Effects of surface passivation on the emission current of gated Si field emitters were investigated by exposing emitter tips to Cl-2 and H-2 plasmas prior to testing. Considerable improvements in the emission characteristics were observed after plasma passivation. The emission current was enhanced and the turn-on voltage was reduced after Cl-2 and H-2 plasma passivation, which corresponds to a work function reduction of 0.5 and 0.9 eV, respectively.