Semiconductor light emitting device in which high-power light output can be obtained with a simple structure including InGaAsP active layer not less than 3.5 microns and InGaAsP and InP cladding

The semiconductor light emitting device includes a semiconductor substrate formed from InP, an active layer, an n-type cladding layer formed from InGaAsP, and a p-type cladding layer formed from InP. The active layer is formed at the upper side of the semiconductor substrate. The n-type cladding layer and the p-type cladding layer are formed so as to hold the active layer therebetween. The semiconductor light emitting device is, given that, a refractive index of the n-type cladding layer is na, and a refractive index of the p-type cladding layer is nb, set so as to be the relationship of na>nb in which the refractive index na of the n-type cladding layer is higher than the refractive index nb of the p-type cladding layer, and due to the distribution of light generated by the active layer being deflected to the n-type cladding layer side, optical loss by intervalence band light absorption at the p-type cladding layer is suppressed, and high-power light output can be obtained.