The optical properties of GaN nanowhiskers with average diameters of 10 to 20 nm formed by photoelectrochemical etching were investigated using photoluminescence (PL) and cathodoluminescence (CL) spectroscopy and imaging. The main donor-bound exciton peak of the etched sample showed a red-shift of 9 meV compared to the unetched sample. CL mapping revealed that the luminescence originated from the surrounding matrix of GaN while the nanowhiskers themselves were non-radiative. copyright The Electrochemical Society.