The influences of annealing temperature in N₂ atmosphere on interfacial chemical properties and band alignment of AlN/Si structure deposited by atomic layer deposition have been investigated based on x-ray photoelectron spectroscopy and spectroscopic ellipsometry. It is found that more oxygen incorporated into AlN film with the increasing annealing temperature, resulting from a little residual H₂O in N₂ atmosphere reacting with AlN film during the annealing treatment. Accordingly, the Si–N bonding at the interface gradually transforms to Si–O bonding with the increasing temperature due to the diffusion of oxygen from AlN film to the Si substrate. Specially, the Si–O–Al bonding state can be detected in the 900 °C-annealed sample. Furthermore, it is determined that the band gap and valence band offset increase with increasing annealing temperature.