This disclosure provides methods and apparatuses for annealing an oxide semiconductor in a thin film transistor (TFT). In one aspect, the method includes providing a substrate with a partially fabricated TFT structure formed on the substrate. The partially fabricated TFT structure can include an oxide semiconductor layer and a dielectric oxide layer on the oxide semiconductor layer. The oxide semiconductor layer is annealed by heating the dielectric oxide layer with an infrared laser under ambient conditions to a temperature below the melting temperature of the oxide semiconductor layer. The infrared laser radiation can be substantially absorbed by the dielectric oxide layer and can remove unwanted defects from the oxide semiconductor layer at an interface in contact with the dielectric oxide layer.