A method for manufacturing oxide thin film transistors includes steps of: forming a gate, a drain electrode, a source electrode, and an oxide semiconductor layer respectively. The oxide semiconductor layer is formed on the gate electrode; the drain electrode and the source electrode are formed at two opposite sides of the oxide semiconductor layer. The method further includes a step of depositing a dielectric layer of silicon oxide, and a reacting gas for depositing the silicon oxide includes silane and nitrous oxide. A flow rate of nitrous oxide is in a range from 10 to 200 standard cubic centimeters per minute (SCCM). Oxide thin film transistors manufactured by above method has advantages of low leakage, high mobility, and other integrated circuit member can be directly formed on the thin film transistor array substrate of a display device.