Abstract: Thin films of substantially pure soluble polythiophenes and oligothiophenes undergo cross-linking and insolubilization upon irradiation with UV/visible light, without additives. Irradiation of thin polymer films through a photomask and subsequent development with solvent leaves a polymeric image of the mask. The resulting .pi.-conjugated polymeric pattern can be rendered electronically conducting by oxidation. The electronic conductivity of these films is high and is similar to that found for oxidized, non-irradiated films. Furthermore, the conductivity can be regulated over eight orders of magnitude by controlled oxidation. Thus, the fabrication of electronically conducting, organic "wires" or "channels" using conventional semiconductor photolithographic techniques can be achieved.