A compact, inexpensive system for high resolution X-ray and gamma ray detection has been developed. A small, cylindrical hybrid circuit includes detector, FET and feedback components mounted on a small thermoelectric cooler. The hybrid mounts to a small enclosure which provides heat sinking and houses the hybrid preamplifier. A novel feedback technique eliminates feedback resistor noise. Resolution with a 7 mm(2) silicon-PIN diode for the 5.9 keV Fe-55 peak is 250 eV FWHM. Other solid state detectors may be used with the XR-100T electronics to meet the requirements of a wide range of applications.