With the x-ray spectroscopy method two groups of semiconducting compounds are investigated. The first group consists of: CdIn2S4 (spinel type structure; (Fd3m-Ok1), CdGa2S4 and HgGa24(the ''defective'' chalcopyrite; (I (4) over bar-S4(2)):). To the second group belong: Tl3TaS4 (that is made of coordinative tetrahedra [TaS4] and of structure units [TIS8]; (I (4) over bar 3m-Td(3))) and isostructural compounds Tl3PS4 and Tl4AsS4 (the structural type K3PS4; (pnma-C2h?(16))). The fluorescent K-emission bands and absorption K-spectra (XANES) of sulphur in compounds investigated are received with the resolution about 0.2 eV. The primary L-2,L-3-emission bands of S have been studied using RSM-500 with resolution 0.4 eV. The electron energy structure of the valence bands are similar in isoelectronic compounds CdIn2S4, CdGa2S4 and HgGa2S4 that follows from the likeness of the forms of the x-ray emission bands in these compounds. At the same time the absorption SK-spectra (XANES) are alike only for CdGa2S4 and HgGa2S4 and differ significantly with SK-spectrum of CdIn2S4, that is due to the difference of S-atom sorroundings in these compounds. The similarity of the forms of all x-ray spectra in isostructural and isoelectronic compounds Tl3PS4 and Tl3AsS4 proves the likeness of the electron-energy structure in these compounds and of the environment of S-atom in these compounds. The emission and absorption spectra of S in Tl3TaS4 differ from ones of Tl3PS4 and Tl3AsS4, that is due to the fact, that Ta-atom is not isoelectronic to atoms of P and As, that results in the difference of S-atom surroundings and the electron-energy structure.
