The objective is to develop a quantitative model for simulating dislocation motion and multiplication in gallium arsenide (GaAs) crystals during growth from the melt by taking the crystallography of slip into account. A constitutive model that couples microscopic dislocation motion and multiplication to macroscopic plastic deformation is employed for developing the model. The density of dislocations in the crystal is predicted by assuming the crystal to be grown under quasi-steady-state conditions. The thermoelastic stresses are calculated from a two-dimensional finite-element analysis, and then transformed into the resolved shear stresses in each slip system for the simulation of dislocation motion and multiplication. A numerical example is presented to verify the validity of the model. The calculated distribution of dislocation density on (001) GaAs wafer shows fourfold symmetry which is consistent with etch pit observations made by Jordan, Caruso, and Von Neida [Bell Syst. Tech. J. 59, 593 (1980)]. Although the emphasis is placed on GaAs, the model can be applied to other electronic and photonic materials.