An 8-nm-thick epitaxial CaF2 layer grown on an n(+)-Si substrate was used as the insulator in a metal-insulator-semiconductor cathode with a 10 mu m(2) emitter region. The fabricated cathodes exhibited two different types of I-V characteristics. The first type showed conventional tunnel emission current of 22 pA at an emitter current of 2.4 mA and an emitter voltage of 7 V. The emitter with the other type of characteristics showed an emission current of 5.6 nA at an emitter current of 2.2 mA and an emitter voltage of 4.5 V but it showed current instability.