A 3D semiconductor device, the device including: a first level including single crystal first transistors, where the first level is overlaid by a first isolation layer; a second level including single crystal second transistors, where the first isolation layer is overlaid by the second level, and where the second level is overlaid by a second isolation layer; a third level including single crystal third transistors, where the second isolation layer is overlaid by the third level, where the third level is overlaid by a third isolation layer, and where the first isolation layer and the second isolation layer are separated by a distance of less than four microns.