We developed highly efficient phosphorescent organic light emitting diodes (PHOLEDs) using iridium(III) complex, fac-tris[4-methyl-2-2(4'-trimethylsilylphenyl)pyridine] [Ir(msippy)3]. PHOLEDs based on Ir(msippy)3 complex exhibit the yellowish-green emission with CIE color coordinates of (0.31,0.64). These device performances were compared with those of the green emitting Ir(ppy)3-based devices. The higher external quantum efficiency (EQE) of 25.6% and the current efficiency of 84.4 cd/A were achieved for Ir(msippy)3-based device. The results show that the complete energy and/or charge transfer from the host to Ir(msippy)3 dopant in the emitting layer (EML) of the device resulted in the higher device efficiencies compared with those of Ir(ppy)3-based devices.