Abstract: A field emission gun in which a field emission tip for generating charged particles is axially aligned with apertures in an intermediate electrode and a main electrode. A field electrode is placed in juxtaposition to the field emission tip for developing a particle generation field. This electrode is located relative to the field emission tip and the intermediate electrode to effect a predetermined focal distance and level of electron beam intensity. Use of a field electrode permits utilization of lower focusing and acceleration voltages and renders the device less sensitive to variations in field emission tip design and performance.