An improved method of forming a semiconducting polymer layer protected by an insulating polymer layer is described. In the method, a material for forming a semiconducting polymer and an insulating polymer are dissolved in a solvent. The blended solution is deposited on a substrate where the semiconducting polymer and insulating polymer segregate. Upon evaporation of the solvent, the semiconducting material forms the active region of a TFT and the insulating polymer minimizes the exposure of the semiconducting polymer to air.