Disclosed herein is a high efficiency light emitting diode. The light emitting diode includes: a semiconductor stack positioned over a support substrate; a reflective metal layer positioned between the support substrate and the semiconductor stack to ohmic-contact a p-type compound semiconductor layer of the semiconductor stack and having a groove exposing the semiconductor stack; a first electrode pad positioned on an n-type compound semiconductor layer of the semiconductor stack; an electrode extension extending from the first electrode pad and positioned over the groove region; and an upper insulating layer interposed between the first electrode pad and the semiconductor stack. In addition, the n-type compound semiconductor layer includes an n-type contact layer, and the n-type contact layer has a Si doping concentration of 5 to 7×1018/cm3 and a thickness in the range of 5 to 10 um.