A thin film transistor comprising at least three terminals consisting of a gate electrode, a source electrode and a drain electrode; an insulator layer and an organic semiconductor layer on a substrate, which controls its electric current flowing between the source and the drain by applying a electric voltage across the gate electrode, wherein the organic semiconductor layer comprises a styryl derivative having a styryl structure expressed by C6H5—CH═CH—C6H5, or a distyryl structure expressed by C6H5—CH═CH—C6H5—CH═CH—C6H5 each without molecular weight distribution. The transistor has a fast response speed (driving speed), and further, achieves a large On/Off ratio getting an enhanced performance as a transistor.