The lateral variation of the emission energy of GaAs masklessly grown on V‐grooved Si is imaged with cathodoluminescence wavelength imaging. This newly developed unique experimental approach allows, for the first time, to directly visualize and quantify the extreme homogeneity of this novel growth mode and the lateral variation of Si impurity incorporation in such semiconductor microstructures. It represents an essential characterization tool for micropatterned optoelectronic monolithic integrated circuits.