Simulation of contrast for small spherical defects in the X-ray beam-induced current (XBIC) mode has been carried out. Under simulations the excess carrier generation function is described by the rigid cylinder with the constant generation rate inside it. The dependence of maximum contrast value on the precipitate depth, diffusion length and effective beam radius is calculated. The XBIC contrast profile as a function of diffusion length, of beam radius and of precipitate depth has been calculated that allows to evaluate the spatial resolution of the technique. The results obtained are compared with those calculated for the EBIC contrast of the same defect. It is shown that in the semiconductor materials with the small diffusion length the XBIC contrast could be comparable with the EBIC one.