Abstract: A method to form a 3D semiconductor device, the method including: providing a first level including first circuits, the first circuits including first transistors and first interconnection; preparing a second level including a silicon layer; forming second circuits over the second level, the second circuits including second transistors and second interconnection; transferring with bonding the second level on top of the first level; and then thinning the second level to a thickness of less than ten microns, where the bonding includes oxide to oxide bonds, and where the bonding includes metal to metal bonds.