The origin of the motion of semiconductors during ion mixing was investigated by studying both the temperature and the atomic mass dependence of moving species in the GexSi1−x/Ni and the GexSi1−x/Pd systems. Ion mixing was performed with 280‐keV Ar ions at temperatures between 30 K and room temperature. The atomic mass of the GexSi1−xalloy was adjusted by changing the concentration of Ge in the alloy. In thermally induced reactions, no preferential motion of Si or Ge was observed. During ion mixing, the atomic flux of Si was observed to be enhanced compared to that of Ge. The atomic flux of the sum of Si and Ge to metal decreases with increasing substrate temperature during mixing and with increasing Ge concentration in the GexSi1−xalloy. From the strong atomic mass dependence of the moving species during ion mixing it is concluded that the origin of the motion of semiconductors under ion mixing conditions is due to the effects of secondary recoils.