Abstract: An LED with undercut includes a first semiconductor layer, an illumination layer, a second semiconductor layer, a first electrode and a second electrode. The first semiconductor layer includes a first area and a second area. A first acute angle is included between a first slanted wall and a first top surface of the first area. The illuminating layer is formed on the second area. The second semiconductor is formed on the illuminating layer. The first and second electrodes are respectively formed on the first top surface and the second semiconductor layer. The first semiconductor layer on the second area, the illuminating layer and the second semiconductor layer on the first semiconductor layer form a MESA structure. The MESA structure includes a second slanted wall adjacent to the first area. A second acute angle is included between the second slanted wall and the first top surface.