A thin film transistor comprises a layer of organic semiconductor material comprising a tetracarboxylic diimide naphthalene-based compound having, attached to each of the imide nitrogen atoms, a substituted or unsubstituted alicyclic ring system, optionally substituted with electron donating 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 an organic thin-film transistor device, preferably by sublimation deposition onto a substrate, wherein the substrate temperature is no more than 100.degree. C.