Planar electron emitters have been fabricated using diamond thin films having a micro-gap. The electronic properties of the diamond thin films were characterized on the basis of the electron emission properties from the gap in the diamond cathode. Extremely low threshold emission, as low as 10 V, was observed from the diamond emitter composed of the continuous thin films and luminescence from phosphor was clearly seen by applying a voltage of 500 V on the anode screen placed 2.5 mm above this device.