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We have fabricated and characterized GaN LED devices whose mesa sidewalls are intentionally made deep and angled. The angled sidewalls efficiently deflect the photons guided laterally along the GaN epitaxial (epi) layer to a direction normal to the surface via total internal reflection. Regardless of the sidewall angle, the sidewall-deflector-integrated (SDI) LEDs exhibit significant enhancement in the light output from the device surface. The largest enhancement, which occurs when the mesa sidewall angle is about 30deg, is greater than 2times. Computer simulations based on ray optics correctly reproduce the sidewall angle dependence of the enhancement factor. Near-field emission patterns as well as space-resolved electroluminescence spectra also support that the enhancement in the light output is due to those additional photons that are guided laterally and deflected by the angled mesa sidewalls.