The thermal annealing effects on a single-field emitter fabricated by beam-assisted processing were investigated from the viewpoint of the leakage current between the gate and cathode. The cathode current of the field emitters before annealing did not show a linear dependence in Fowler-Nordheim (FN) plots due to the leakage current. However, the current showed a linear dependence in FN plots at and above 200 degrees C. Thermal annealing increased the emission efficiency. The maximum efficiency was almost 100% after annealing at 750 degrees C. The percentage of working nanoelectron sources was also increased by annealing T >= 500 degrees C. The postannealing is effective in reducing the leakage current of the field emitters because of the removal of contaminants arising from the beam-induced process. (c) 2005 American Vacuum Society.