In this paper, the crystal structure, microstructure, thermoelectric properties and figure of merit (zT) of highly pure higher manganese silicide (HMS) alloys are reported and discussed without the bias generally introduced by impurities in published results. The alloys were produced by both solid-state reaction diffusion assisted by spark plasma sintering and conventional arc melting in order to evaluate the effect of the process on the microstructure and on the resulting properties of HMS. The effect of Ge addition is also explored. Properties diagram for thermoelectric materials is displayed to assess the performance of un-doped and Ge-doped HMS alloys in comparison with the state of the art. Electrical conductivity and zT at 500 °C of the HMS alloys studied here exceed published properties achieved with similar alloys, providing new process options for reliable, affordable and efficient thermoelectric applications.