A structure includes a semiconductor-on-insulator (SOI) substrate including a semiconductor substrate, a buried insulator layer over the semiconductor substrate, and an SOI layer over the buried insulator layer. At least one polycrystalline active region fill shape is in the SOI layer. A polycrystalline isolation region may be in the semiconductor substrate under the buried insulator layer. The at least one polycrystalline active region fill shape is laterally aligned over the polycrystalline isolation region, where provided. Where provided, the polycrystalline isolation region may extend to different depths in the semiconductor substrate.