A methodology for the passivation of bottom-gate thin-film transistors (TFTs) utilizing zinc–tin–oxide as the channel layer and silicon dioxide as the passivation layer is presented. This methodology involves annealing of the TFT after channel layer deposition and an additional anneal after thermal evaporation of a SiO₂ passivation layer. Passivated zinc–tin–oxide TFTs possess electrical characteristics equivalent to those of unpassivated, air-exposed devices. In contrast, TFT electrical performance is dramatically degraded if a zinc–tin–oxide TFT is covered with a dielectric layer and does not undergo both types of anneal. In addition to silicon dioxide, successful passivation of zinc–tin–oxide TFTs is accomplished using thermally evaporated calcium fluoride, germanium oxide, strontium fluoride, or antimony oxide as passivation dielectrics.