Ruthenium arsenide is made p-type by the addition of germanium, and it exhibits a large substitution range without affecting the stability. A series of RuAs2−xGex with x = 0.02, 0.04, 0.08, 0.16, 0.32, and 0.64 shows the saturation limit of Ge to be between 0.16 and 0.32. The electrical contribution to the thermoelectric performance is greatly improved with a power factor of 1.03 mW/(m K2). However, the substitution does not affect the rigidity of the lattice, as the Debye temperature remains around 420 K, which means that the thermal conductivity remains high resulting in a modest maximum zT of 0.11.