The investigation of the sensitivity of a ionization-type semiconductor photographic system with high-resistivity cathode of large diameter (40-60 mm) is described. A photosensitive GaAs cathode with a resistivity of 10(6) Omega cm, has been studied. With a gas discharge gap formed by a dielectric separator with the thickness ranging from 40 to 60 mu m, a discharge has been formed in air at pressures from 20-760 Torr. The cathode was irradiated on the back with light in a particular wavelength range that mns used to control the photoconductivity of the material. The semiconductor material was found to stabilize the discharge. A local change of the resistance inhomogeneity is determined by a local change of discharge radiation intensity. The assessment of the resistance distribution is then based on analysis of the discharge radiation, visualized by a photograph taken through the SnO2 film. Means of increasing the sensitivity and improving the working characteristics are proposed.