An x-ray and gamma-ray radiation energy imaging device has its semiconductor detector substrate and semiconductor readout/processing substrate both mounted on opposite sides of, and electrically communicating through, an intermediate substrate. The substrates are all substantially planar with the top plan perimeter of the semiconductor readout/processing substrate falling within the top plan shadow perimeter of the corresponding semiconductor detector substrate with which it electrically communicates. Additionally, all of the readout/processing circuitry contacts of the semiconductor readout/processing substrate are disposed on the surface of the semiconductor readout/processing substrate that electrically communicates with the intermediate substrate. Substantially all electrical communication to and from the semiconductor readout/processing substrate is routed through the intermediate substrate. The intermediate substrate is a printed circuit board or similar construct. The electrical contacts between the semiconductor substrates and the intermediate substrate are accomplished using bump-bonds, conductive adhesive bonds, conductive adhesive films or a combination thereof. One or two dimensional planar arrays of semiconductor readout/processing substrates and corresponding semiconductor detector substrates can be mounted on a single intermediate substrate using "tiling" techniques known in the art to form a mosaic radiation imaging device of increased active imaging area and reduced/minimized imaging dead area.