In a Group III nitride compound semiconductor light-emitting device which outputs lights from a semiconductor plane, about 1.5 .mu.m in height of a Group III nitride compound semiconductor projection part 150, which is made of Mg-doped p-type GaN having Mg doping concentration of 8.times.10.sup.19/cm.sup.3 and is formed through selective growth, is formed on a p-type contact layer (second p-layer) 108. And a light-transparency electrode 110 is formed thereon through metal deposition. The Group III nitride compound semiconductor projection part 150 makes a rugged surface for outputting lights and actual critical angle is widened, which enables to improve luminous outputting efficiency. And because etching is not employed to form the ruggedness, driving voltage does not increase.