The fabrication of solar cell grade silicon (SOG-Si) feedstock involves processes that require direct contact between solid and liquid phases at near equilibrium conditions. Knowledge of the phase diagram and thermochemical properties of the Si-based system is therefore important for providing boundary conditions in the analysis of processes. A self-consistent thermodynamic description of the Si-Ag-Al-As-Au-B-Bi-C-Ca-Co-Cr-Cu-Fe-Ga-Ge-In-Li-Mg-Mn-Mo-N-Na-Ni-O-P-Pb-S-Sb-Sn-Te-Ti-V-W-Zn-Zr system has recently been developed by SINTEF Materials and Chemistry. The assessed database has been designed for use within the composition space associated with SoG-Si materials. The thermochemical database has further been extended to calculate the surface tensions of liquid Si-based melts. In addition to thermochemical and phase equilibrium calculation, several surface-related properties (temperature and composition gradients, surface excess quantity etc.) are able to simulate simultaneously using the database. The databases can be regarded as the state-of-art equilibrium relations in the Si-based multicomponent system.