A method realizes a thin film organic electronic device integrated on a substrate and includes an organic material layer and an organic thin film transistor or OTFT transistor. The method comprises: depositing the organic material layer on the substrate, the organic material layer being a conductive organic polymer; patterning by a soft-lithographic procedure the organic material layer to create a reduced portion in order to make a channel area of the OTFT transistor; masking the organic material layer by covering with a cover mask a source area and a drain area of the OTFT transistor; irradiating by ultraviolet radiation to deactivate exposed portions of the organic material layer defining the source area, the drain area and the channel area; depositing on the organic material layer a semiconductor layer; and creating on the semiconductor layer a gate area of the OTFT transistor.