According to one embodiment, a semiconductor light emitting device includes a stacked structural body, a first electrode, and a second electrode. The stacked structural body includes a first semiconductor layer of a first conductivity type, a second semiconductor layer of a second conductivity type, and a light emitting portion. The stacked structural body has a first major surface on a side of the second semiconductor layer. The first electrode is provided on the first semiconductor. The second electrode is provided on the second semiconductor layer. The first electrode includes a first pad portion and a first extending portion that extends from the first pad portion along a first extending direction. The first extending portion includes a first width-increasing portion. A width of the first width-increasing portion along a direction orthogonal to the first extending direction is increased from the first pad portion toward an end of the first extending portion.