The plasma contact effect on the spectral characteristics of GaAs photodetector longitudinal photoconductivity has been investigated. The photodetector studied was a GaAs:Cr high-resistivity (rho = 10(7) Omega cm) plate of thickness d = 1 mm and diameter similar to 30 mm. One electrode (thin Ni layer) was deposited on the plate surface and the other electrode (SnO2 film) was separated from the plate surface by the gas discharge air gap. The constant voltage applied to the electrodes was higher than the breakdown voltage. The photodetector was illuminated both from the side of Ni-contact and through plasma contact. The measured spectral characteristics of the photocurrent were different in the strong absorption region. When the photodetector was illuminated through plasma contact the photocurrent was 1.5-2 times higher than that for the Ni-contact illumination. The observed phenomenon in the ionization photographic system can be explained by the change of surface recombination velocity of nonequilibrium carriers in the GaAs semiconductor photodetector due to bombardment of the semiconductor surface by plasma.