The Ta2O5 film prepared on silicon by RF sputtering has been used as a gate insulator for the top-contact field-effect transistors fabricated with poly(2-methoxy-5-(2'-ethylhexyloxy)1,4-phenylenevinylene) (MEH-PPV) or pentacene. Good transistor characteristics have been obtained with saturation at low drive voltages (about -3 V) and with hole mobilities of 5.2 x 10(-4) cm(2)/VS (MEH-PPV) and 0.8 cm(2)/VS (pentacene).