A device for detecting inhomogeneities in high-resistivity poly(N-vinylimidazole) polymeric semiconductor film of large diameter (40-60 mm) is described. A measurement of homogeneity is realized by recording the spatial distribution of the gas discharge glow intensity between two parallel electrodes. The polymeric films with a resistivity of 10(6)-10(8) Omega cm (thickness 40-80 mu m) in a planar gas discharge cell, have been studied. A gas discharge gap has been formed by a dielectric separator with the thicknesses ranging from 15 to 25 mu m. A discharge has been realized in air at pressures from 60-760 Torr. The possibilities of the visualization have been evaluated, i.e. a local change of the resistance inhomogeneity is determined by a local change of discharge glow intensity the resolution of which is determined by method of its recording.