Semiconductor structures. The semiconductor structures include two silicon-on-insulator wafers having devices fabricated therein and bonding them back to back utilizing the buried oxide layers or bonding them back to back utilizing an inter-substrate dielectric layer and a bonding layer between the buried oxide layers. The structures include contacts formed in the upper wafer to devices in the lower wafer and wiring levels formed on the upper wafer. The lower wafer may include wiring levels. The lower wafer may include landing pads for the contacts. Contacts to the silicon layer of the lower wafer may be silicided.