Microfabricated field emitters have shown the potential for very high current densities (> 100 A/cm(2)) and total emission currents (> 1 A). However, realizing this potential has been elusive, primarily because these cathodes exhibit insufficient emission uniformity over an emitter array. In this article we report the development of an in situ processing method based on emitter tip self-heating during operation that is shown to improve emission uniformity between emitter tips. Two tips differing in emission current by three orders of magnitude for a given voltage as fabricated are shown to be essentially identical in their emission characteristics after controlled pulsing to very high emission current. When the method was applied to a 50 000 tip array, it produced 300 mA of emission (40 A/cm(2)). The experimental arrangement prevented advancing to higher emission levels due to space charge limitations. It is expected that 1 A of emission at similar to 100 A/cm(2) is possible with appropriate modifications to the experimental apparatus. (c) 2005 American Vacuum Society.