We improved carrier injection of organic field-effect transistors (OFETs) by utilizing organic/inorganic hybrid electrodes. One of thiophene/phenylene co-oligomers (TPCOs) was employed as an organic semiconductor crystal layer and as a part of hybrid electrodes with Ag. As the volume ratio of Ag: TPCO changed from 1: 0 to 1: 3, the carrier mobility was enhanced up to similar to 10(-1) cm(2)/Vs even after exposure to the atmosphere. This value was 1.5 times larger than that of the OFET with electrodes made of only Ag, which suggests that the introduction of the hybrid electrodes improved the carrier injection from the electrode into the organic crystal.