A thin film transistor comprises a layer of organic semiconductor material comprising a tetracarboxylic diimide naphthalene-based compound having, attached to one or both of the imide nitrogen atoms, a substituted or unsubstituted heterocycloalkyl ring system. Such transistors can further comprise spaced apart first and second contacts 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 200° C.