Transistor emission characteristics from a monolithic diamond vacuum triode fabricated by a self-aligning gate technique have been studied and modeled. The anode emission current of diamond triodes has been modeled per the Fowler-Nordheim triode equation and an empirical model for the emission transport factor described. The model was applied to two different diamond field emission triodes with distinct emission characteristics. A procedure for modeling parameter extraction is developed and demonstrated. The modeling results agree well with the experimental data. The empirical model can be incorporated into programs for field emission device simulation. (C) 2003 American Vacuum Society.