Silicon p–n diodes have proved to be excellent soft x-ray detectors due to their high sensitivity, nominally flat response, and long term stability. Advances in fabrication techniques have overcome many of the limitations of older silicon diodes by minimizing the thickness of the surface dead layer which would otherwise absorb low energy x-ray photons. Silicon photodiodes with extremely thin (80 Å) surface dead layers are now available.1 One of these diodes has been characterized for spectral sensitivity at x-ray photon energies of 163 eV and 1.4 keV using a laser produced plasma soft x-ray source. Measurements have also been made to characterize the impulse response using fourth harmonic laser light from a short pulse (80 ps full width half maximum) NdYAG laser.