A thin film transistor comprises a layer of organic semiconductor material comprising a tetracarboxylic diimide 3,4,9,10-perylene-based compound having, attached to each of the imide nitrogen atoms a carbocyclic or heterocyclic aromatic ring system substituted with one or more fluorine-containing groups. Such transistors can further comprise spaced apart first and second contact means or electrodes in contact with said material. Further disclosed is a process for fabricating ac thin film transistor device, preferably by sublimation or solution-phase deposition onto a substrate, wherein the substrate temperature is no more than 100.degree. C.