An electron beam with an energy as low as 5 eV and a current of 0.1 mA was produced by an electron source with a 10,000-tip silicon-based field emitter array (Si-FEA). In order to decelerate the electrons, we have designed an electrostatic lens system for the divergent beam extracted from the FEA. Spatial distribution of the electrons was investigated by a fluorescent screen with a multiple channel plate. Finally, space charge neutralization of low-energy and high-current ion beam was demonstrated with the present electron source.