Thermo-Calc software was used to produce the phase diagram the silicon-phosphorous (Si-P) binary system. The calculations were performed at a pressure of 1 bar and temperature range 300-2000 K. The temperature versus mass percent phase diagram showed three phases; Si (Diamond A4) solid solution, liquid, and SiP. There are two single phase regions and six double – phase regions. The melting points of Diamond Si and red P were determined and found to be Tm (Si) = 1687.0 K (1413.85°C), and Tm(red P) = 704.25 K (431.1 °C), which are close to those found in the literature. There is eutectic point at T = 1404.01 K (1130.86 °C) and Si mass percent of 65%. The metallic SiP line appears at 47.552 Si mass percent, and the melting point of SiP is Tm(SiP) = 1412.41 K (1139.26 °C).