We evaluated the characteristics of single Si field emitters (Si-FEs) from the perspective of their use in electron guns. Since the current fluctuation of Si-FEs strongly depends on the product of vacuum pressurePand emission currentI, just as it does for conventional cold field emitters (CFEs), the mechanism of fluctuation was assumed to be similar to that of CFE. Such fluctuations are divided into two regions, the boundary was virtually equal to CFEs, at approximately3×10−12 Pa A.However, unlike as for CFEs, the emission current of Si-FEs drops abruptly after a certain duration. We found that the integral ofPIwith the duration time (PITintegral) is almost constant (approximately1×10−8 Pa A s) in various conditions and therefore assume that it correlates with the emission area of the emitter tip. The current leakage between emitter and gate electrode was found to be caused because of their small size. Responsible for this leakage are hydrocarbon contamination layers that were generated by emitted electrons or backscattered electrons on the surface of the insulating layer. Finally, we fabricated a miniaturized electron gun with Si-FEs and succeeded in obtaining SEM images with electrons that were emitted from the Si-FEs.