Integrated Circuit Structure with Substrate Isolation and Un-Doped Channel

The present disclosure provides a semiconductor structure. The semiconductor structure includes a fin structure formed on a substrate; a gate stack formed over the fin structure; source/drain regions over the substrate and disposed on opposing sides of the gate stack; a channel region defined in the fin structure and underlying the gate stack, wherein the channel region is un-doped; and a buried isolation layer disposed vertically between the channel region and the substrate, wherein the buried isolation layer includes a compound semiconductor oxide.