Blue InGaN micro-size light emitting diodes (LEDs) with diameters from 3 to 70 mu m have been fabricated. An ion implantation technique and a 12 mu m electro-ridge were used to simplify the fabrication processes. The 3-70 mu m LEDs exhibiting a large emission of photon blue shift (40-240 meV) were observed in electro-luminescence (EL) spectra. The dependence of the blue shift on size is studied. The characteristics of the micro-size LEDs are also investigated numerically with the use of an advanced physical model of semiconductor devices (APSYS). The experimental measurements and simulation results are in close agreement for maximum blue shift. Base on the simulation, the difference between blue shift caused by band filling effect and red shift caused by lateral carrier confinement are approximately the same. Hence, the maximum blue shift increases when the size of micro-size LED increases because of decreased red shift resulted from thermal effect. (C) 2006 Elsevier Ltd. All rights reserved.