A simple one-step focused ion beam (FIB) etching technique was used to fabricate a microlens array on the back side of sapphire substrate of a GaN blue light emitting diode (LED) with a nominal lens diameter of 2.7 mu m. The microlens array can enhance the electroluminescence of GaN/sapphire blue LED to about 1.6 times at 20 mA. (c) 2006 The Electrochemical Society.