Abstract The phase diagram of the Sr–Si system has been investigated across almost the whole composition range (0–75 at.% Si) using differential thermal analysis (DTA), metallographic analysis, X-ray diffraction and electron microscopy. Four intermediate phases exist: Sr 2Si (PbCl 2-type), Sr 5Si 3 (Cr 5B 3-type), SrSi (CrB-type) and the dimorphic SrSi 2 compound. The low-temperature form α-SrSi 2 is cubic, SrSi 2-type, and the high-temperature form β-SrSi 2 is tetragonal with the α-ThSi 2 structure-type. For this last phase a solid solubility range, from about 62.0 to 66.7 at.% Si, has also been found. Four eutectics occur in the system: at about 3 at.% Si and 745 °C, 44 at.% Si and 1110 °C, 61 at.% Si and 1055 °C, 74 at.% Si and 1045 °C.