The aim of this paper is to calculate/simulate electron trajectories in the diode or triode configuration for the cold cathode of a miniature electron gun. An experimental setup with millimeter-scale planar electrodes was prepared to help us estimate the necessary parameters, which were consequently used as the input data for the EGUN software. This software was used to calculate electron trajectories and the beam currents of electron guns and beam optics. This program has an additional subroutine for calculating Fowler-Nordheim emission of the electrons. The calculated results are very promising, giving a parallel or converging beam for the triode configuration. The described method could even be used eventually for simulating micro-emitters for field-emission displays. (c) 2006 American Vacuum Society.