Semiconductors with magnetic response at room temperature are sought for spintronics in solid-state devices. Among possible materials for this applications, the magnetic response of FeSi and doped FeSi have produced contradictory results at the nanoscale and more precise measurements and deeper studies are needed to clarify its potential capabilities. For that reason, in this work, single nanowire measurements of ferromagnetic semiconducting FeSi and Mn-doped FeSi nanostructures have been performed using magnetic force microscopy and electron holography. Results obtained confirm the presence of magnetic domains at room temperature with a magnetic moment per Fe atom of [Formula: see text] Spin polarized density functional calculations confirm a net magnetic moment between [Formula: see text] in Fe surface atoms with an estimated Curie temperature of 417 K by means of the molecular field approximation. The nanowires present a crystalline B20 cubic structure as confirmed by x-ray diffraction and high-resolution electron microscopy. Their electrical transport measurements confirm p-type nature and thermal activation. A remanent magnetization of 1.5 × 10-5 emu and 0.5 × 10-5 emu was measured at room temperature for FeSi and Mn-doped FeSi respectively, with spin freezing behavior around 30 K for the Mn-doped nanowires.