A semiconductor light emitting device, comprising: a first semiconductor layer of a first conductivity type including a nitride semiconductor; a second semiconductor layer of a second conductivity type provided on a -direction side of the first semiconductor layer, the second semiconductor layer including the nitride semiconductor; and a light emitting layer provided between the first semiconductor layer and the second semiconductor layer, the light emitting layer including the nitride semiconductor, the light emitting layer including: a first well layer provided between the first semiconductor layer and the second semiconductor layer; a second well layer provided between the first well layer and the first semiconductor layer; and a first barrier layer (41 a) provided between the second well layer and the first well layer to contact the second well layer and the first well layer, an In composition ratio of the first barrier layer being lower than an In composition ratio of the first well layer and an In composition ratio of the second well layer, characterized in that the first barrier layer including: a first portion provided between the first well layer and the second well layer, the first portion being in contact with the second well layer, the first portion having a first thickness in a first direction from the first semiconductor layer toward the second semiconductor layer; and a second portion provided between the first portion and the first well layer, the second portion having a first region and a second region, the first region being in contact with the first portion, the second region provided between the first region and the first well layer, the second region being in contact with the first well layer, the first region having a first In composition ratio higher than an In composition ratio of the first portion, the second region having a second In composition ratio lower than the first In composition ratio. a first semiconductor layer of a first conductivity type including a nitride semiconductor; a second semiconductor layer of a second conductivity type provided on a -direction side of the first semiconductor layer, the second semiconductor layer including the nitride semiconductor; and a light emitting layer provided between the first semiconductor layer and the second semiconductor layer, the light emitting layer including the nitride semiconductor, the light emitting layer including: a first well layer provided between the first semiconductor layer and the second semiconductor layer; a second well layer provided between the first well layer and the first semiconductor layer; and a first barrier layer (41 a) provided between the second well layer and the first well layer to contact the second well layer and the first well layer, an In composition ratio of the first barrier layer being lower than an In composition ratio of the first well layer and an In composition ratio of the second well layer, characterized in that a first well layer provided between the first semiconductor layer and the second semiconductor layer; a second well layer provided between the first well layer and the first semiconductor layer; and a first barrier layer (41 a) provided between the second well layer and the first well layer to contact the second well layer and the first well layer, an In composition ratio of the first barrier layer being lower than an In composition ratio of the first well layer and an In composition ratio of the second well layer, characterized in that the first barrier layer including: a first portion provided between the first well layer and the second well layer, the first portion being in contact with the second well layer, the first portion having a first thickness in a first direction from the first semiconductor layer toward the second semiconductor layer; and a second portion provided between the first portion and the first well layer, the second portion having a first region and a second region, the first region being in contact with the first portion, the second region provided between the first region and the first well layer, the second region being in contact with the first well layer, a first portion provided between the first well layer and the second well layer, the first portion being in contact with the second well layer, the first portion having a first thickness in a first direction from the first semiconductor layer toward the second semiconductor layer; and a second portion provided between the first portion and the first well layer, the second portion having a first region and a second region, the first region being in contact with the first portion, the second region provided between the first region and the first well layer, the second region being in contact with the first well layer, the first region having a first In composition ratio higher than an In composition ratio of the first portion, the second region having a second In composition ratio lower than the first In composition ratio.