Strongly adhered layers of the compound with the primary amino group directed toward the solution were obtained at the gold surface by chronoamperometric electroreduction of 4-aminoethylobenzenodiazonium salt (AEBD) in acetonitrile solution at appropriately selected potential. The used techniques (EQCM, AFM, EIS, PM, IRRAS) showed that the nature and thickness of formed aminoethylophenyl layer strongly depend on the potential applied to the electrode. Electroreduction of AEBD salt at a potential more negative than -0.6 V (vs Ag/AgCl) leads to about monolayer on the gold surface. Additionally, such a layer was very tight and uniform. The electrochemical measurements indicate that the efficient and precise attachment of biomolecules to the aminoethylophenyl layer is only possible when this layer is formed at appropriate potential. This was shown for ss- and dsDNA.