Organic-soluble DNAs bearing chalcone moieties were synthesized by using purified natural sodium DNA. In addition to the chalcone-containing DNA homopolymer (CcDNA), a copolymer (CTMADNA-co-CcDNA) was synthesized. They were employed as gate insulators for fabricating organic thin-film transistors. An organic semiconductor (5,5′-(9,10-bis((4-hexylphenyl)ethynyl)anthracene-2,6-yl-diyl)bis(ethyne-2,1-diyl)bis(2-hexylthiophene; HB-ant-THT) was deposited on the photocrosslinked DNA-based gate insulators via a solution process. Interestingly, the resulting TFT devices had extremely high field-effect mobilities, and their corresponding transfer curves indicated low hysteresis. The carrier mobility of the device with HB-ant-THT deposited on the CTMADNA-co-CcDNA gate insulator was the best, i.e., 0.31 cm2 V−1 s−1 (Ion/Ioff=1.0×104).