In this work, using a Ge film as a buffer layer, highly strained Si epitaxial growth on Ge/Si(100) has been investigated. Epitaxial growth of strained Si films on 84 %-relaxed Ge/Si(100) is achieved using ECR plasma CVD without substrate heating. Especially for the thickness of 1.7 nm, strain amount in the strained Si reaches as high as 4 % and it is thermally stable even at 500degC