The cluster-size distribution of Si1-xFex alloys was statistically analyzed. The samples were grown by MBE on Si(100) and investigated by atomic force microscopy and scanning electron microscopy. The microscopy observations revealed the Stranski-Krastanov growth of irregular islands whose size-distribution had a bimodal structure with a power-law decrease superimposed on a bell-shaped distribution peak around the mean cluster size. We found that the values of the power-law exponent and the peak position change with the investigated growth parameters, i.e, the growth temperature and the alloy composition. We explain the Si1-xGex cluster-size distribution in terms of a modified Family-Meakin growth model.