A semiconductor light emitting device composed of an n-type cladding layer, an n-type guide layer, an active layer, a p-type guide layer, and a p-type cladding layer which are sequentially laminated on a substrate. The p-type guide layer is formed from ZnSSe mixed crystal doped with nitrogen. That side of the p-type guide layer which is adjacent to the p-type cladding layer is a p-type semiconductor region in which the concentration of nitrogen is 2.times.10.sup.17 cm.sup.-3, and that side adjacent to the active layer is an intrinsic semiconductor region. The p-type cladding layer is formed from ZnMgSSe mixed crystal doped with nitrogen. That side of the p-type cladding layer which is adjacent to the p-type guide layer is the low-concentration region in which the concentration of nitrogen is 1.times.10.sup.17 cm.sup.-3 which is lower than the concentration at which the rate of activation begins to decrease. The opposite side is the high-concentration region in which the concentration of nitrogen os 2.times.10.sup.17 cm.sup.-3 which is lower than the seturated concentration.
The semiconductor light emitting device has a prolonged life owing to the adequate concentration of p-type impurity in the p-type cladding layer.