Semiconductor devices include a semiconductor substrate with a stack structure protruding from the semiconductor substrate and surrounded by an isolation structure. The stack structure includes an active layer pattern and a gap-filling insulation layer between the semiconductor substrate and the active layer pattern. A gate electrode extends from the isolation structure around the stack structure. The gate electrode is configured to provide a support structure for the active layer pattern. The gate electrode may be a gate electrode of a silicon on insulator (SOI) device formed on the semiconductor wafer and the semiconductor device may further include a bulk silicon device formed on the semiconductor substrate in a region of the semiconductor substrate not including the gap-filing insulation layer.