Novel mixed five-membered heterocyclic (furan, thiophene, and thiazole) oligomers containing a thiazolothiazole ring system have been investigated as active materials of organic field-effect transistors (OFETs). The field-effect moblities of 10(-4)- 10(-3) cm(2)/VS were obtained for the furyl derivatives and their FET performances as p-type semiconductors are presented as the first examples of FET behavior of oligomers including furan rings.