An SOI substrate is fabricated by providing a substrate having a sacrificial layer thereon, an active semiconductor layer on the sacrificial layer remote from the substrate and a supporting layer that extends along at least two sides of the active semiconductor layer and the sacrificial layer and onto the substrate, and that exposes at least one side of the sacrificial layer. At least some of the sacrificial layer is etched through the at least one side thereof that is exposed by the supporting layer to form a void space between the substrate and the active semiconductor layer, such that the active semiconductor layer is supported in spaced-apart relation from the substrate by the supporting layer. The void space may be at least partially filled with an insulator lining.