According to one embodiment, a semiconductor light emitting device includes a semiconductor laminated body provided on a semiconductor substrate. The semiconductor laminated body includes a light emitting layer. The light emitting layer includes a quantum well structure made by alternately laminating n (an integer of not less than 1) well layers and (n+1) barrier layers and emits light with a peak wavelength of 650 nm to 1000 nm. Each of the well layers has a thickness of smaller than 15 nm. Each of the barrier layers has a thickness of 15 nm to 50 nm.