A group III nitride substrate has a semi-polar primary surface. A first cladding layer has a first conductivity type, and comprises aluminum-containing group III nitride. The first cladding layer is provided on the substrate. An active layer is provided on the first cladding layer. A second cladding layer has a second conductivity type, and comprises aluminum-containing group III nitride. The second cladding layer is provided on the active layer. An optical guiding layer is provided between the first cladding layer and the active layer and/or between the second cladding layer and the active layer. The optical guiding layer comprises a first layer comprising Inx1Ga1-x1N (0≦x1