We report a comparative study on the performance of InGaN/AlGaN multiple quantum well (MQW) light emitting diodes (LEDs) fabricated on c- and a-plane sapphire substrates, respectively. It was found that the LEDs grown on a-plane sapphire substrates exhibited enhanced electroluminescence intensity, decreased double crystal X-ray diffraction linewidth, reduced etching pit density, and smaller ideality factor compared to those deposited on c- plane sapphire substrates. The improved LED characteristics are attributed to threading dislocation density decrement inside the LEDs due to the reduced mismatch between LED structure and a-plane sapphire substrate. (c) 2006 The Electrochemical Society.