The GOES-8 solar x-ray sensor (XRS) detects solar x-rays in two wavelength bands of approximately 0.5 to 3 angstrom and 1 to 8 angstrom. The XRS uses a dual ion chamber design with beryllium windows and Xenon or Argon gas fills to provide the x-ray detection, and which determine the wavelength response functions. GOES spacecraft before GOES-8 were spinning, and the previous XRS design used this property to measure the solar x-rays as a 'pulse' above the ambient particle background during the time when the XRS FOV scanned across the sun. GOES-8 and later spacecraft are three-axis stabilized, and the XRS now views the sun constantly from a mount on the solar panel yoke. This puts a severe requirement on the XRS for shielding of the ion chamber, since the background current form ambient particles must be will below the current from the design threshold x-ray fluxes. The design and calibration of the XRS is described, as are results from electron irradiation which were used to verify the immunity to ambient particle fluxes.