Bottom gate thin-film transistors were fabricated using solution processed IGZO channel layers with various gallium composition ratios that were annealed on a hot plate. Increasing the gallium ratio from 0.1 to 0.6 induced a threshold voltage shift in the electrical characteristics, whereas the molar ratio of In:Zn was fixed to 1:1. Among the devices, the IGZO-TFTs with gallium ratios of 0.4 and 0.5 exhibited suitable switching characteristics with low off-current and low SS values. The IGZO-TFTs prepared from IGZO films with a gallium ratio of 0.4 showed a mobility, on/off current ratio, threshold voltage, and subthreshold swing value of $0.1135cm^2/V{cdot}s$, ${sim}10^6$, 0.8 V, and 0.69 V/dec, respectively. IGZO-TFTs annealed at $300^{circ}C$, $350^{circ}C$, and $400^{circ}C$ were also fabricated. Annealing at lower temperatures induced a positive shift in the threshold voltage and produced inferior electrical properties.