Both sides of a semiconductor-on-insulator substrate are utilized to form MOSFET structures. After forming first type devices on a first semiconductor layer, a handle wafer is bonded to the top of a first middle-of-line dielectric layer. A lower portion of a carrier substrate is then removed to expose a second semiconductor layer and to form second type devices thereupon. Conductive vias may be formed through the buried insulator layer to electrically connect the first type devices and the second type devices. Use of block masks is minimized since each side of the buried insulator has only one type of devices. Two levels of devices are present in the structure and boundary areas between different types of devices are reduced or eliminated, thereby increasing packing density of devices. The same alignment marks may be used to align the wafer either front side up or back side up.