The generation and propagation of threading dislocations in GaAs grown on Si was studied by transmission electron microscopy. This study was conducted by analyzing dislocation structures in GaAs at various growth stages. The dislocation structure changes as the GaAs grows from initial islands to a thick film. These changes are explained by the following physical processes: (1) nucleation of dislocations in GaAs islands, (2) generation and propagation of threading dislocations during coalescence of initial GaAs islands and their subsequent growth, and (3) bending of threading dislocations under misfit‐strain force and their interactions. The second process results in threading dislocations extending from the interface to the surface in thin films. The third process causes an improvement in near‐surface quality in thick films. The iplication of this study in confining threading dislocations to near the interface is discussed.