A series of large crystals of α-Al(Mn,Fe)Si has been analyzed using microprobe, X-ray diffraction, pychnometer and electrical devices The cubic phase α-Al(Mn,Fe)Si has a density varying from 3520 kg/m3 to 3620 kg/m3. When iron is increased from 1.9 wt% to 20.8 wt%, the content of silicon is reduced from 10.7 wt% to 8.6 wt%. The phase had a low electrical resistivity, 2x10-6 Ωm. Large crystals of α-AlMnSi had a large Seebeck coefficient viz. 42 µV/⁰C. All the crystals were n-semiconductors. A new model for α-AlMnSi has been proposed where Si-atoms are connected in hexagonal rings around 0,0,0 and ½,½,½. The rings are linked by Mn and Si atoms, all covalent bonded. According to this model the ideal α-AlMnSi crystals have 24 Mn-, 18 Si- and 96 Al-atoms in the unit cell. Fe+Al can substitute for Mn + Si atoms in the unit cell. Vacancies can form on Mn-sites.