The junction temperature of homoepitaxial green and blue GaInN/GaN quantum well light emitting diode (LED) dies is analyzed by micro-Raman, photoluminescence, cathodoluminescence mapping, and forward-voltage methods and compared to finite element simulations. Dies on GaN substrate and sapphire were analyzed under variable drive current up to 200 mA (246 A/cm(2)). At 100 mA, dies on bulk GaN remain as cool as 355 K(83 degrees C) while dies on sapphire heat up to 477 K (204 degrees C). The efficiency droop and spectral line shift in green LEDs with increasing current density can now be separated into electrical and thermal contributions. (C) 2009 Elsevier B.V. All rights reserved.