Cu 4 GeS 4 was synthesized by the solid state reaction of the constituent binary chalcogenides at 8303C. Its crystal structure was determined on the basis of X-ray data of a nonmerohedral twinned crystal: monoclinic P2 1 /c, a β«Ψβ¬ 9.790(2), b β«Ψβ¬ 13.205(2), c β«Ψβ¬ 9.942(3) A > , β«Ψβ¬ 100.90(2)3, Z β«Ψβ¬ 8. The re5nement of 164 parameters with 1373 data converged to R 1 β«Ψβ¬ 0.058 [for I > 2 (I)], wR 2 β«Ψβ¬ 0.176 (all data), and a twin fraction of 0.274(4). The crystal structure may be described as a monoclinic variant of the Cu 4 SnS 4 type. It is characterized by a three-dimensional framework based on a hexagonal close-packing of sulfur atoms. The Cu and Ge atoms are distributed in an ordered manner over 5/8 of the tetrahedral voids, with half of the Cu atoms distorted into triangular sites. The structure was compared with that of Cu 4 SnS 4 , and the di4erence was ascribed to the formation of more triangular Cu sites in Cu 4 GeS 4 . An extended HuK ckel tightbinding band calculation was performed to analyze the electronic structure, and electrical resistivity measurements con5rm the expected semiconducting behavior of Cu 4 GeS 4 .