A new acentric sulfide Y4Si3S12 was grown by a high temperature vapor transport reaction. The crystal structure of Y4Si3S12 was determined by single crystal X-ray diffraction. Y4Si3S12 is isostructural to La4Ge3S12. The three dimensional structure of Y4Si3S12 is constructed by [Y1S7] augmented triangular prisms, [Y2S6] triangular prisms and [SiS4] tetrahedra through sharing vertices and edges. Y4Si3S12 is revealed as an indirect bandgap semiconductor with a calculated bandgap of 2.1 eV, which is close to 2.5(1) eV experimentally measured by UV-Vis. The Y−S interactions and Si−S interactions are predicated to be strong ionic bonds and covalent bonds, respectively, by electron localization function coupled with crystal orbital Hamilton population calculations. Y4Si3S12 is verified by DFT calculations to have moderate birefringence, with incident 1900 nm laser, Δn=0.09. DFT calculations also predicted that Y4Si3S12 possesses moderate second harmonic generation response with χ111=15.03 pm/V. The nonlinear optical properties of Y4Si3S12 are mainly contributed by Y−S interactions revealed by DFT calculations.