The flat metal-insulator-semiconductor (MIS) electron emitter is a simple design, allowing easy manufacture. The emitters are relatively insensitive to environment, allowing them to operate in poorer vacuum conditions than are necessary for oxide thermionic or microtip field emitters. In most literature reports, MIS and metal-insulator-metal devices are limited in emission current (< 0.001 A/cm(2)) by their low efficiencies (<= 0.1%). We have observed emission currents as high as 2 - 10 A/cm(2) at efficiencies from 3% - 10%. Our best results are from emitters comprised of 5-7.5 nm gold/15 nm SiO2/100 nm polysilicon/n(++) doped silicon substrate. The roles of each component of the flat emitter were investigated. The polysilicon serves a dual role: Bumps on its surface act as field-enhanced emission sites while the bulk of the film behaves as a self-adjusting ballast resistor preventing run away emission from any one emission site. The thin gold layer self-assembles into a nanomesh with > 400 pores/mu m(2) through which electrons are emitted. Energy distribution and angular divergence of emitted electrons were measured. A coherent explanation of emission including the origination of the divergence is presented. Pros and cons of the MIS emitter and potential application are discussed. (c) 2005 American Vacuum Society.