A circuit model is proposed to analyze the driving characteristics of the carbon nanotube field emission triode. In the model, the cur-rent gain magnitude, the cutoff frequency, and the transition frequency can be calculated, and the result is confirmed by PSPICE simulation. In addition, the parameters that affect the cutoff frequency and the transition frequency are discussed, which include capacities, inductances, and transconductance. The influence of the traverse time of electrons on the triode's frequency performance will play an important role in the range of very high frequency. (c) 2007 American Vacuum Society.