The application of cathodoluminescence spectral mapping to the characterisation of a range III-nitride semiconductor structures is described. Details are presented of the instrumentation developed to carry out such measurements using an electron probe micro-analyser. The spatial resolution of the luminescence data is ∼100 nm. The technique is enhanced by the ability to simultaneously perform X-ray microanalysis and electron imaging. Results are presented from epitaxially laterally overgrown GaN and InGaN/GaN structures using both single-layer SiO2 and multilayer SiO2/ZrO2 masks. Effects of strain and microcavity formation are resolved. Application of the technique to InGaN epilayers shows spatially-dependent shifts in the peak wavelength of the luminescence spectrum which correlate directly with microscopic variations in the indium content. Regions emitting at lower energy and with decreased intensity are shown to have higher InN contents, mirroring equivalent macroscopic observations. Finally the spectral mapping technique is used to analyse the luminescence from micron-scale selectively grown III-N pyramids, indicating possible formation of quantum dots at the sharp tips. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)