The electrical, optical and photoelectric properties of organic/inorganic semiconductors heterostructures are investigated depending upon the interface microrelief morphology modified by chemical etching of GaAs. Polishing andanisotropic etchants were used to change it from flat to microtextured(quasigrating-type). The p/n-heterostructures were fabricated by the vacuumevaporation of thin (similar to50 nm) pentacene or phthalocyanine of lead filmson modified surface of n-GaAs crystals. A considerable decrease of the optical reflectance and increase of the photosensitivity by a few (1.5-4) times have been obtained for microtextured heterostructures with respect to the flat ones. The results emphasize the importance of GaAs surface chemical microtexturing to future developments of the photocells, based on organic semiconductor/GaAs heterojunction.