A nitride based semiconductor light emitting device is revealed. The light emitting device includes a light emitting epitaxial layer, a P-type electrode and a N-type electrode. The P-type electrode and the N-type electrode are disposed on the light emitting epitaxial layer. The light emitting device features on that the N-type electrode is arranged on the inner side of the P-type electrode. The P-type electrode extends toward the N-type electrode along the edge of the light emitting epitaxial layer and the N-type electrode extends inward along the inner side of the P-type electrode. By means of the electrode pattern with special design, the light emitting area of the light emitting device is increased.