A thin film transistor comprising at least three terminals consisting of a
gate electrode, a source electrode and a drain electrode; an insulating
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 heterocyclic compound containing a
nitrogen atom formed by condensation between five member rings each
having a nitrogen atom at their condensation sites or between a five
member ring and a six member ring each having a nitrogen atom at their
condensation sites. The transistor became to have a fast response speed
(driving speed), and further, achieved a large on/off ratio getting an
enhanced performance as a transistor.