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.