Initial stage of Cu-phthalocyanine (CuPc) organic molecules deposition in UHV on atomically clean CdS(0001) substrate was studied by using Total Current Spectroscopy (TCS), Auger Electron Spectroscopy (AES) and the work function (WF) measurements. Evolution of the WF, the density of unoccupied states (DOUS) located 0-25 eV above the vacuum level and the chemical composition were measured during the film deposition (in situ) in the range of deposit thickness of 0-10 nm. Formation of the "interface layer" of the variable composition 2-3 monolayers thick was observed. The role of the chemical interactions between organic and inorganic semiconductors and the diffusion of metalloid (S) component were discussed.