We investigated the lateral thickness modulation of InGaAs layers grown on width-modulated GaAs wire structures in selective area metalorganic vapor phase epitaxy (SA-MOVPE). The InGaAs layer was formed for various GaAs buffer layer thicknesses and growth conditions. Growth of the InGaAs layer was enhanced, which is caused by the atom migration of group III atom from sidewall facets. The result indicates that the lateral thickness modulation along the [1 1 0] direction becomes more abrupt if one suppresses the diffusion on the top (0 0 1) terrace surface and the supply of growth species from sidewall facets in the transition region.