Strain modulation of β-FeSi2 by Ge doping was investigated. By solid-phase growth of [a-Si/a-Fe0.4Si0.5Ge0.1]n layered structures, the [a-SiGe/β-FeSi2-xGe
]n multi-layered structures (n=1, 2, 4) were formed after annealing at 700 °C. From the analysis of the x-ray diffraction spectra, it was found that β-FeSi1.3Ge0.7 strained by 0.4–0.5 % was formed for the sample with n=1. This value corresponded to the band gap modulation of 30 meV based on the theoretical calculation. The strains decreased with increasing n, which was due to that segregation of Ge atoms from the a-Fe0.4Si0.5Ge0.1 layers to the a-Si layers became significant with increasing n. After annealing at 800 °C, agglomeration of β-FeSi2 occurred, and nanocrystals of relaxed β-FeSi2 and c-Si0.7Ge0.3 were formed. These new structures are useful for formation of opto-electrical devices.