A field effect transistor is provided which comprises an organic semiconductor layer comprising a compound having a monobenzoporphyrin skeleton represented by the general formula (1): ##STR00001## wherein R.sub.1 and R.sub.2 are independently selected from the group consisting of a hydrogen atom, a halogen atom, a hydroxyl group, and alkyl, alkenyl, oxyalkyl, thioalkyl, alkyl ester and aryl groups each having 1 to 12 carbon atoms with the proviso that adjacent R.sub.1 may be the same or different and adjacent R.sub.2 may be the same or different and that at least two of R.sub.2 are not hydrogen atoms; R.sub.3 is a hydrogen atom or an aryl group; and M denotes two hydrogen atoms, a metal atom or a metal oxide.