There is provided a semiconductor light emitting device in which light emitting efficiency is totally improved in case of emitting a light having a short wavelength of 400 nm or less by raising internal quantum efficiency by enhancing crystallinity of semiconductor layers laminated and by raising external quantum efficiency by taking out the light emitted by preventing the light emitted from being absorbed in the substrate or the like, as much as possible. In case of laminating ZnO compound semiconductor layers (2 to 6) so as to form a light emitting layer forming portion (7) for emitting the light having a wavelength of 400 nm or less on a substrate (1), a substrate composed of MgxZn1-xO (0≦x≦0.5) is used as the substrate (1).