Total current electron spectroscopy (TCS) is applied as a key experimental technique to studies of electronic structure of organic semiconductor films interfacing inorganic semiconductors. Thin films of Cu-phthalocyanine (CuPc) were thermally deposited in UHV on CdS(000-1) and GaAS(100) substrates. The surface potential, the surface work function and the structure of unoccupied electron states (DOUS) located 5-25 eV above the Fermi level (E(F)) was monitored during the film deposition, using an incident beam of low-energy electrons according to the TCS method. Auger electron spectroscopy (AES) was used to monitor atomic composition of the surfaces under study. Electronic work function of the CuPc films changed during the film deposition until it reached a stable value 4.5 +/- 0.1 eV at the film thickness 8-10 nm. The deposition of the CuPc under 1.5 nm resulted in formation of the intermediate DOUS structures that were different for the cases of the two substrates used in the study. Fragments of the CuPc molecules were found to constitute mainly the intermediate deposit layers. Along with the increase of the deposit thickness to 8-10 nm, the intermediate DOUS structures were replaced by the DOUS structure typical for the CuPc film, although the S, Ga and As atoms migrated from the substrates were present in the CuPc film. Electron charge transfer layer at the CuPc/GaAs interface extended more than 5 nm from the GaAs surface, while the interaction at the CuPc/CdS interface resulted in band bending in the CdS subsurface region. (C) 2004 Elsevier B.V. All rights reserved.