MoW, SiN_x, and IZO layers were used as gate electrode, gate insulator, and source and drain electrodes, respectively. IGZO active channel layers of ~45 nm were deposited at 450 °C using a spin‐coating method. It was observed that the TFT without any Ga content operates in the depletion mode with a deep threshold voltage (V_th) of −10.32 V. The spin-coated active channel film, without any Ga, is very effective as a conductor. As the Ga content is increased in the IGZO, the V_th is shifted in the positive direction and the off current of the TFT dropped below 10⁻¹⁰A of I_DS. This results in an improvement of the on‐to‐off current ratio (I_on/off). At a Ga/Zn ratio of 0.5 (below 10¹⁶ cm⁻³), the TFT device displays optimal performance. The linear mobility (µ_lin), V_th, I_on/off, and subthreshold voltage (S) were estimated to be 0.86 cm²/Vs, 6.89 V, ∼10⁶, and 0.63 V/decade, respectively. From these results, it is apparent that the Ga content in the IGZO is a critical factor in determining the IGZO TFT operating characteristics as well as the electrical properties of solution IGZO films. Although it is not demonstrated here, for a Ga/Zn ratio above 0.5, the positive shift of turn on the voltage clearly occurs and the on current and mobility of the TFT was drastically reduced, much like a semi‐insulator.