Low profile, side-emitting LEDs are described, where all light is efficiently emitted within a relatively narrow angle generally parallel to the surface of the light-generating active layer. The LEDs enable the creation of very thin backlights for backlighting an LCD. In one embodiment, the LED is a flip chip with the n and p electrodes on the same side of the LED, and the LED is mounted electrode-side down on a submount. A reflector is provided on the top surface of the LED so that light impinging on the reflector is reflected back toward the active layer and eventually exits through a side surface of the LED. A waveguide layer and/or one or more phosphors layers are deposed between the semiconductor layers and the reflector for increasing the side emission area for increased efficiency. Side-emitting LEDs with a thickness of between 0.2-0.4 mm can be created.