We report on the development of a practical realization of a vacuum magnetic sensor device. The proposed device differs from those proposed in previous work [M. I. Marques, P. A. Sarena, D. Nicolaescu, and A. Correia, Solid-State Electron. 45, 977 (2001); K. Uemura, S. Kanemaru, and J. Itoh, J. Micromech. Microeng. 11, 81 (2001)] in that it is lateral, with the cathode, gate, and anode electrodes all lying in a plane parallel to that of the silicon substrate. By using the ion trajectory modeling program SIMION, we show that this structure allows the sensor device to have a variable sensitivity mode of operation, in which the sensitivity can be controlled through application of a voltage to the device substrate. This device allows a magnetic sensing system to be created that can measure magnetic field strengths over many orders of magnitude. (C) 2004 American Vacuum Society.