Ternary ruthenium ferrites (Ba,Sr)Fe2 +/- xRu4 -/+ xO11 exhibit long-range ferromagnetic order well above room temperature along with favorable narrow-gap semiconducting properties. Electronic structure and physical properties can be tuned by simple chemical substitution of two elements, Fe and Co, or by varying the relative concentration of 3d and 4d elements within the homogeneity range. These promising properties within a single structural family open up a host of potential device applications.