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Townsend-type discharge in a modified gas discharge cell with coupled narrow gaps between a high-resistivity semiconductor plate and two planar electrodes is experimentally studied in the range of gas pressure 28-352 torr for various interelectrode distances (d1 = 50 μm, d2 = 50 - 320 μm). The effect of various diameters on the photodetector area to the discharge (D = 9 - 12 - 15 mm) are considered as well. It is observed that Townsend discharge is unstable at low current densities for certain experimental parameters. The temporal dynamics of the current fluctuations is measured around I = 50 μA. Interactions of plasmas with surfaces and space charge effects in many cases are the main reason for the nonlinear effects in gas discharges with increasing current.