DNA molecules immobilization on n-type single silicon was investigated. Electronic states were studied by measuring voltage-ampere characteristics (VAC) of Au-(n-Si) contacts with DNA molecules on the interface. It is showed that strong DNA fixation is observed in the presence of magnesium ions in solution. Molecules conformation on the surface is determined by the degree of the substrate hydrophobicity. Devel- oped method of DNA immobilization allows to create model systems with the molecules in the form of molecular mesh or ropes depending on irradiation intensity. Formed on the silicon surface molecular struc- tures have different effect on the electrical properties of Au-DNA-(n-Si) contacts. Presence of molecular mesh on the Schottky diode interface makes its VAC similar to ideal diode. The ropes lead to electronic state density increasing.