Ultra-soft X-ray emission spectroscopy (USXES) and X-ray diffraction were applied for the investigation of solid phase interaction in thin-film structure Pt/Si(111). Vacuum annealing at temperatures from 530 to 770 K for periods from 10 to 240 min resulted in the formation of Pt12Si5/Si, Pt12Si5/PtSi/Si and PtSi/Si structures. After irradiation with a xenon lamp in air, a Pt+ SiO2/Pt12Si5/PtSi/Si thin-film structure was observed. Ultra-soft X-ray emission spectra of platinum N-6,N-7 and silicon L-2,L-3 from Pt12Si5 and PtSi thin films were obtained. The results are compared with spectra measured on elementary platinum and silicon.