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Ferromagnetic semiconductors are of interest due to the unusual combination of physical properties and because if tunable they may offer opportunities for studying magnetic quantum critical points. Here, we illustrate an approach for studying suitable materials based on itinerant magnetism, different from conventional magnetic semiconductors. We show that p-type FeAs₂ is an example. The complex non-parabolic band structure of this material leads to a ferromagnetic instability when doped, while at the same time allowing for a modest transport effective mass. This leads to an analogy between magnetic semiconductors and thermoelectric materials.