The quaternary diamond-like semiconductor, Cu2ZnSiS4, was synthesized by high-temperature solid-state synthesis at 1000 °C. High-resolution synchrotron X-ray powder diffraction of this product revealed the presence of two polymorphs. This data confirms that the known α-Cu2ZnSiS4 exists with the wurtz-stannite structure in the noncentrosymmetric space group Pmn21. The new polymorph, β-Cu2ZnSiS4, crystallizes in the noncentrosymmetric space group Pn with a = 6.134092(6) Å, b = 6.392752(5) Å, c = 7.421228(8) Å, β = 90.056(1)°, Z = 2, χ2 = 5.554, Rp = 0.0857 and wRp = 0.1173. Electronic structure calculations performed for both polymorphs indicate direct bandgaps of 1.3 and 1.7 eV at the Γ-point, respectively.