In this study, we fabricated zinc tin oxide (ZTO) thin-film transistors (TFTs) using a sol–gel solution at a low annealing temperature of 350 °C. We found that the combination of conventional hot plate annealing and microwave irradiation was effective for achieving high performance of ZTO-TFTs. Solution-processed ZTO-TFTs prepared at 350 °C by microwave irradiation showed enhanced device characteristics of 1.84 cm2 V-1 s-1 mobility and a 106 on/off current ratio. X-ray photoelectron spectroscopy analyses confirmed that residual hydroxyls in solution-processed ZTO films can be decomposed at low temperatures by microwave irradiation. Low-temperature microwave-assisted processing makes ZTO TFTs promising for use in flexible, transparent electronics.