Highly selective oxidation of an AlInN interlayer buried in a GaN matrix is demonstrated. This technique was successfully applied to form current apertures in III-nitride light-emitting diodes (LEDs). GaN LEDs were grown by metal-organic vapor phase epitaxy with a lattice-matched AlInN layer inserted in the n-doped region of the device. Mesas were etched by Cl-2/Ar reactive ion etching to give access to the AlInN sidewalls. The sample was then oxidized anodically in a nitrilotriacetic acid solution. Using this technique, the AlInN layer was oxidized laterally up to 22 mu m deep while the surrounding GaN layers were kept unaffected. It was subsequently demonstrated that the oxidized AlInN layers are insulating and are therefore suitable for lateral current confinement in optoelectronic devices. (C) 2005 American Institute of Physics.