The thermoelectric properties between 10 and 300 K and the growth of single crystals of n-type and p-type GeBi4Te7, GeSb4Te7 and Ge(Bi1−xSbx)4Te7 solid solution are reported. Single crystals were grown by the modified Bridgman method, and p-type behavior was achieved by the substitution of Bi by Sb in GeBi4Te7. The thermopower in the Ge(Bi1−xSbx)4Te7 solid solution ranges from −117 to +160 μV K−1. The crossover from n-type to p-type is continuous with increasing Sb content and is observed at x ≈0.15. The highest thermoelectric efficiencies among the tested n-type and p-type samples are ZnT = 0.11 and ZpT = 0.20, respectively. For an optimal n–p couple in this alloy system the composite figure of merit is ZnpT = 0.17 at room temperature.