The band alignment and interface reaction at the AlN/MnS interface were investigated by hard X-ray photoelectron spectroscopy. The AlN/MnS/Si (100) stack structure is a candidate of a template substrate for the non-polar GaN growth on a Si (100) substrate. For the band alignment of AlN/MnS, the AlN film on MnS buffer layer had a type II band structure. The conduction band offset from AlN to MnS was -0.59 eV. For the interface stability at the AlN/MnS interface, the S 2s spectra showed undistinguishable change regardless of the growth temperature of AlN. The nitrogen and sulfur defects were formed. The Fermi level position did not show the growth temperature dependence, although the depletion layer was formed at the interface of AlN and the Fermi level moved in-gap direction. The growth temperature of AlN did not affect the band offset of AlN/MnS. The AlN/MnS interface was chemically and electrically stable interface.