A device for rapid visualization of electrical and spatial inhomegeneities of a semi-insulating GaAs (rho greater-than-or-equal-to 10(6) OMEGA cm) is described. This visualizer is a modification of the ionization type photographic system in which a semiconducting plate is placed between transparent plane parallel electrodes in the gas discharge cell. The gas discharge gaps are formed between free surfaces of the semiconductor and electrodes. When a voltage is applied to the electrodes a discharge luminescence glows in the gap under uniform infrared illumination of the semiconductor. The uniformity of glowing over the semiconductor area is determined by electrical homogeneity and infrared absorptivity of the material. The main discharge glow patterns on both sides and after chemical etching are similar, which reflects the fact that the structural defects are continuous within the plate. The observed patterns give information about EL2 centres in the GaAs semiconductor. Technical data of the ionization-type visualizer of electrical inhomogeneities in a semiconducting plate are given.