Highly transparent organic thin-film transistors (OTFTs) based on pentacene have been demonstrated successfully. By inserting one layer of metal oxides between the transparent electrodes and the semiconductor, the device performance was enhanced dramatically. Meanwhile, the average transmittance, which is as high as 72.2%, in the visible region has been realized. The high transmittance is among the highest values reported for thin-film transistors made of organic semiconductors. Furthermore, from the results of the transfer line method, it is realized that device enhancement is contributed from reduction of the contact resistance.