Ga doping in indium zinc oxide (IZO)-based amorphous-oxide semiconductors (AOSs) promotes the formation of oxide-lattice structures with oxygen vacancies at low annealing temperatures, which is essential for acceptable thin-film-transistor performance (see figure). The mobility dependence on annealing temperature and AOS composition are analyzed and the chemical role of Ga is clarified, as required for solution-processed, low-temperature-annealed AOSs.