The fluctuation of the emission current from carbon nanotube field emitter arrays (CNT FEAs) grown on silicon emitters was investigated as a function of total emission current and ambient pressure. The ratio of amplitude of short-term fluctuation DeltaI and average emission current I-ave strongly depended on I-ave. The relationship DeltaI/I(ave)proportional toI(ave)(-1/2) was found. This relationship showed that the average emission current Iave is proportional to the number of active carbon nanotube emitters. The effect of vacuum pressure on the emission properties was examined by adjusting the pumping speed of the turbomolecular pump. The emission current at fixed voltage was affected by the adsorption of gas species and amounts. (C) 2004 American Vacuum Society.