AbstractNonlinear electrical transport processes in a semiconductor‐gas discharge structure with semi‐insulating GaAs are studied for a wide range of gas pressures, interelectrode distances and different diameters of the photocathode areas. A primary destabilization of homogeneous state observed in a planar dc‐driven structure is due to nonlinear transport properties of GaAs photocathode. GaAs samples present N‐shaped negative differential conductivity under high‐electric fields and the presence of the deep electronic levels of defects, the so‐called EL2 centers, gives rise to the N‐type‐NDC of the material, as a consequence, to low‐frequency oscillations in current when a dc voltage of a high enough magnitude is applied to a GaAs photocathode. It is important to note that we have experimentally investigated the above‐mentioned nonlinear electrical characteristics of GaAs by a new‐suggested method and our experimental findings are obviously in good agreement with estimated results reported by other independent authors. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)