The 800°C isothermal section of the Zn–Si–P ternary system was determined using optical microscopy, scanning electronic microscopy coupled with energy dispersive X-ray spectroscopy, and X-ray diffractometry. One ternary intermetallic compound ZnSiP2 was found in the present study. Thermodynamic description of the Zn–P binary system was obtained from experimental data by means of CALPHAD technique, and the artificial miscibility gap in the liquid region has been avoided. On the basis of the literature data for thermodynamic assessment of the Zn–Si and Si–P systems and the present work on the Zn–P system, the phase diagram calculation for the Zn–Si-P system was carried out. In the inferred phase relations of the Zn–Si–P system at 450°C, ZnSiP2 equilibrates with all the solution phases and intermetallic compounds.