With the aim of facilitating the high performance printed In-Ga-Zn-O (IGZO) thin-film transistors (TFTs), we present the heretofore unrecognized chemical methodology for tailoring the chemical structures of printable IGZO semiconductors through incorporation of ethylene glycol in sol–gel derived precursor solutions. With the optimal composition of ethylene glycol, the device performance of TFT employing the printed IGZO semiconducting layer annealed at 400 °C is significantly improved with the field-effect saturation mobility of 4.9 cm2 V−1s−1. In addition, by lowering the contact resistance between the source/drain electrode and printed IGZO semiconducting layer, the device performance is further improved with the field-effect saturation mobility of 7.6 cm2 V−1s−1.