Applying angle resolved photoemission and scanning tunneling microscopy (STM) during different stages of epitaxial growth of HfS2 on WSe2 allows an evaluation of the electronic valence band spectra as a function of position z perpendicular to the interface. In combination with photon energy dependent photoemission measurements of clean WSe2 and HfS2 samples, mapping k(perpendicular to) dispersions of valence bands' reliable values for the valence band maxima (VBM) have been obtained. Upon different stages of growth, the valence band maximum can thus be traced during the build up of the interface giving an accurate value for the valence band offset of this heterojunction.