A linear position sensitive small‐angle x‐ray detector has been developed which utilizes a directly exposed self‐scanning photodiode array cooled to liquid nitrogen temperature to reduce fixed pattern noise. Direct exposure of the array improves the overall sensitivity to 8 keV photons by an order of magnitude over photoconversion techniques. With this improvement in sensitivity, the photodiode array has been effectively used to detect x rays from weakly scattering biological molecules in solution. The slit‐like geometry of the photodector elements ideally matches that of a Kratky collimator employed with a low‐flux x‐ray source to enhance greatly the data collection rate. The detective quantum efficiency and stability of the detector have been determined while taking small‐angle scattering measurements of proteins and the results are quantitatively applied to characterize the performance of the instrument.