The growth of an InGaN/GaN double heterostructure (DH) was attempted on a stripe patterned GaN grown on a (111) Si substrate by selective area metal organic vapor phase epitaxy. The cathode luminescence (CL) spectroscopy at 4 K suggests that we have an InGaN wire on the (0001) apex. Analysing the CL spectra, we found that the In composition is not uniform on the (1-101) facet, which was attributed to the diffusion of Ga on the facets. But the phenomenon depended on the TMIn (In source gas) flow rate and a uniform In composition was achieved under a certain flow rate. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)