When a Si(Li) solid‐state energy dispersive detector is used to collect x‐ray photons with energies below 2 keV the characteristic peaks in the spectrum show significant deviations from the ideal Gaussian shape observed for higher energy photons. This effect is due to incomplete collection of the charge deposited by the incident photon in the diode. The magnitude of this effect, and the resultant distortion of the spectrum, can be computed by means of a Monte Carlo simulation which models the detector in terms of the three parameters which characterize it, junction depth, diffusion length, and surface recombination velocity. For values of these parameters typical of commercial detectors it is found that the incomplete charge correction can be as high as 30% for a line such as NK&agr;at 400 eV. By matching simulated and experimental spectral shapes, quantitative corrections for each x‐ray line of interest can be computed. The results suggest that alternative design strategies for detectors might permit a higher quality of performance to be achieved at low energies.