A thin film transistor comprises a layer of organic semiconductor material comprising an organic semiconductor material that comprises an aryl dicarboxylic acid diimidazole-based compound. 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 150° C.