A semiconductor light-emitting element includes: an n-type clad layer of an n-type aluminum gallium nitride (AlGaN)-based semiconductor material provided on a substrate; an active layer of an AlGaN-based semiconductor material provided on the n-type clad layer and configured to emit deep ultraviolet light having a wavelength of not shorter than 300 nm and not longer than 360 nm; and a p-type semiconductor layer provided on the active layer. The n-type clad layer is configured such that a transmittance for deep ultraviolet light having a wavelength of 300 nm or shorter is 10% or lower.