Provided is a field effect transistor having an organic semiconductor layer, in which the organic semiconductor layer contains at least a tetrabenzo copper porphyrin crystal and has peaks at two or more of Bragg angles (2.theta.) in CuK.alpha. X-ray diffraction of 8.4.degree..+-.0.2.degree., 10.2.degree..+-.0.2.degree., 11.8.degree..+-.0.2.degree., and 16.9.degree..+-.0.2.degree., and the tetrabenzo copper porphyrin crystal comprises a compound represented by the following general formula (1). ##STR00001## (Wherein R.sub.2's each represent a hydrogen atom, a halogen atom, a hydroxyl group, or an alkyl group, oxyalkyl group, thioalkyl group, or alkylester group having 1 to 12 carbon atoms, and R.sub.3's each represent a hydrogen atom or an aryl group.).