Abstract: An electron beam from a scanning electron microscope, or X-rays from an external X-ray source, impinges on a material sample surface thereby causing the generation of fluorescent X-rays characteristic of the elements present in the sample. An improved energy dispersive X-ray detector system for materials analysis, based on a monolithically fabricated thermal detector array and solid state refrigeration system, is described. The detector array converts the X-ray photons to heat, and the heat is measured as a rise in temperature by thermistors in the individual detector elements in the array. The small detector elements in the array are kept at a low temperature so as to achieve an energy resolution of less than 5 eV, and the multiple elements in the array insure that a sufficient X-ray count rate for normal materials analysis is achieved.