It is shown that growth of smooth layers of (AlGa)As on GaP by liquid phase epitaxy (LPE) can be achieved if the GaP substrate surface possesses a certain degree of roughness when growth starts. This roughness can be introduced by various methods, including preferential chemical etching orin situmelt‐back, but the best surface morphology of the epitaxial layer is obtained after mechanical lapping of the substrate. This striking phenomenon is attributed to an increase of the density of nuclei which results in a more uniform distribution of the grains characteristic for this system with large lattice mismatch.