The absolute x‐ray response of 18 EG&G Ortec partially depleted silicon surface‐barrier diodes (SBDs) have been measured at 8 and 17.5 keV. In addition we have examined the x‐ray response of four Tennelec and two United Detector Technology partially depleted SBDs. The variation in response to 8 keV x rays, for which the optical depth is about five, is comparatively slight (≲12%). The variation in response to 17.5 keV x rays, for which the optical depth is only ∼0.7, is comparatively large (∼100%). These variations are mainly attributable to differences in the SBD physical thicknesses, and thus to differences in optical depth. At both 8 and 17.5 keV the diodes respond linearly to large variations in incident flux (over three orders of magnitude). This linearity, and the diode x‐ray response in general, is insensitive to large changes in the detector bias voltage; thus the depletion depth, proportional to the square root of the bias voltage, does not play a critical role in determining the x‐ray sensitive depth. It is important to emphasize that this finding is contrary to the commonly held belief that the x‐ray sensitive depth is equivalent to the depletion depth. In addition this result has a direct bearing on both SBD and PIN detectors intended for fully depleted operation, but used in an underbiased mode such that they are actually partially depleted. We conclude that SBDs have attractive features for quantitatively measuring x radiation from high‐intensity sources for whichh&ngr;≳10 keV.