The transient response properties of nitrogen‐doped amorphous InGaZnO (a‐IGZO:N) thin film transistors (TFTs) improved first and then became worse with the N 2 flow rate increasing, where the best one occurred at N 2 flow rate=1 sccm. A theoretical model was proposed based on the measurement results of transfer curves and positive bias stresses, indicating that the change of trap states in a‐IGZO:N TFTs, rather than the variation of their field‐effect mobility, should dominate the transient response properties of devices.