Affords a semiconductor light-emitting device in which a decrease in external quantum efficiency has been minimized even at high current densities. In a semiconductor light-emitting device (11), a gallium nitride cladding layer (13) has a threading dislocation density of 1×107 cm−2 or less. An active region (17) has a quantum well structure (17a) consisted of a plurality of well layers (19) and a plurality of barrier layers (21), and the quantum well structure (17a) is provided so as to emit light having a peak wavelength within the wavelength range of 420 nm to 490 nm inclusive. The well layers (19) each include an un-doped InXGa1-XN (0