A semiconductor radiation detector is provided for improved performance of pixels at the outer region of the crystal tile. The detector includes a semiconductor single crystal substrate with two major planar opposing surfaces separated by a substrate thickness. A cathode electrode covers one of the major surfaces extending around the sides of the substrate a fraction of the substrate thickness and insulated on the side portions by an insulating encapsulant. An exemplary example is given using Cadmium Zinc Telluride semiconductor, gold electrodes, and Humiseal encapsulant, with the side portions of the cathode extending approximately 40-60 percent of the substrate thickness. The example with CZT allows use of monolithic CZT detectors in X-ray and Gamma-ray applications at high bias voltage. The shielding electrode design is demonstrated to significantly improve gamma radiation detection of outer pixels of the array, including energy resolution and photopeak counting efficiency. The detector has performance of detector leakage current density less than 6 nA/mm.sup.2 at a bias potential of substantially 1400V, and responsive to gamma radiation such that the energy resolution full width half maximum of more than 90% of the pixels is less than 6%.