A ZnO based semiconductor light emitting device includes: a first semiconductor layer containing ZnO1-x1Sx1; a second semiconductor layer formed above the first semiconductor layer and containing ZnO1-x2Sx2; and a third semiconductor layer formed above the second semiconductor layer and containing ZnO1-x3Sx3, wherein an S composition x1 of the first semiconductor layer, an S composition x2 of the second semiconductor layer and an S composition x3 of the third semiconductor layer are so selected that an energy of the second semiconductor layer at the lower end of a conduction band becomes lower than both energies of the first and third semiconductor layers at the lower end of the conduction bands, and that an energy of the second semiconductor layer at the upper end of a valence band becomes higher than both energies of the first and third semiconductor layers at the upper end of the valence bands.