A method of GaN epilayers quality characterization based on room-temperature luminescence transient studies under deep-trap saturation regime is demonstrated. Recent applications of the method for carrier lifetime measurement in GaN epilayers grown by various techniques are reviewed. The contributions of radiative and nonradiative recombination of carriers in highly excited GaN are distinguished. Possibilities of further improvement of the materials quality are discussed. (c) 2005 Elsevier B.V. All rights reserved.