Emission stability is the most stringent requirement for a field emitter array (FEA) in practical applications. When fluctuating events occur stochastically, the fluctuation in electron emission reduces with where N is the number of individual cathodes. So, the total current of the FEA is expected to be stable. However, the fluctuation does not necessarily occur stochastically, and the mode of fluctuation of each individual microtip is different from tip to tip. We observed the fluctuation of each microtip by use of an emission microscope. The behaviors are classified due to the emission mode. As a result of observation, the modes of fluctuation can be classified in two types. One has a dependence IP product, which is the product of the total current and pressure, and the other has not. To explain the former fluctuation, we propose a model where ion bombardment is due to desorbed gas molecules from the gate hole side of the emitting microtip. The model successfully explains the measured results. However, the latter mode of fluctuation cannot be explained by using this model. High-energy ion bombardment from a phosphor screen may be the origin of the latter mode of fluctuation. © 2003 American Vacuum Society.