A method of making a transistor having first and second electrodes, a semiconductive layer, and a dielectric layer; said semiconductive layer comprising a semiconductive polymer and said dielectric layer comprising an insulating polymer; characterised in that said method comprises the steps of: (i) depositing on the first electrode a layer of a solution containing material for forming the semiconductive layer and material for forming the dielectric layer; and (ii) optionally curing the layer deposited in step (i); wherein, in step (i), the solvent drying time, the temperature of the first electrode and the weight ratio, of (material for forming the dielectric layer): (material for forming the semiconductive layer) in the solution are selected so that the material for forming the semiconductive layer and the material for forming the dielectric layer phase separate by self-organisation to form an interface between the material for forming the semiconductive layer and the material for forming the dielectric layer.