A semiconductor substrate and a manufacturing method therefore, and a semiconductor device using the semiconductor substrate comprise a strained Si region and unstrained Si region formed at substantially the same level. In an aspect of the invention, a semiconductor substrate is provided by comprising a support substrate, a first semiconductor region including a first silicon layer formed above the support substrate, a second semiconductor region including a strained second silicon layer formed above the support substrate, a surface of the second silicon layer being formed at substantially the same level as a surface of the first silicon layer, and an insulating film at an interface between the first semiconductor region and the second semiconductor region.