Si transport in the melt during Czochralski (Cz) growth of Ge1-xSix bulk crystals has been simulated within a 3D unsteady approach using two models of Si sources. The effect of the rod number on Si supply to the crystallization front is discussed. The crystallization front geometry is computed taking into account crystallization temperature varying with Si concentration. The predicted geometry is compared with experimental data. To study the effect of 3D unsteady melt motion, the results are compared with 2D axisymmetric computations of Si transport. (C) 2006 Elsevier B.V. All rights reserved.