A miniature tetrode system, according to F. Burstert, D. Winkler and B. Lischke [Microelectron. Eng. 31 (1996) 95], for the generation of a low-voltage electron probe was investigated and further developed. The tetrode system consists of a Schottky cathode and a miniaturized lens, composed of three conventional electron microscopical apertures, which are used as electrodes. We tested two configurations with different aperture thicknesses and bore diameters experimentally and also made simulations of these lenses. Two kinds of middle electrodes, a flat and a top-hat aperture, were used. In most cases the experimental data show a good agreement with the theoretically predicted values of the examined tetrode system.