Abstract: A method for coating a planar surface (5) of a semiconductor or insulator (3) with a polymer film according to a given pattern. The substrate to be coated constitutes one electrode (3) in an electrolytic cell whose electrolyte (2) contains monomers of said polymer. The substrate and the monomers are selected such that electrolytic oxidation or reduction occurs when a voltage is applied across the cell electrodes (3, 4) simultaneous with an area of the surface (5) to be coated being irradiated with radiation having energy larger than the energy gap between the valence band and conduction band of said substrate. The irradiation is performed with a sharply defined beam (10) simultaneous with a relative motion of said beam and the substrate surface (5) thereby making the polymer film of the desired pattern. The polymer, for example, is polypyrrole formed by electro-oxidation of a pyrrole monomer in an electrolytic solution containing pyrrole monomer and tetraethylammonium tetrafluoroborate in acetonitrile.