It has a structure in which an active layer (5) that emits light by electric current injection is sandwiched between an n-type cladding layer (4) and a p-type cladding layer (6) made of materials having a larger band gap than the active layer (5), wherein the active layer (5) is made, for example, of Cd.sub.xZn.sub.1-xO (0.ltoreq.x<1). It is further more preferable if the cladding layers (4), (6) are made, for example, of Mg.sub.yZn.sub.1-yO (0.ltoreq.y<1). This narrows the band gap of the ZnO materials, and an oxide semiconductor capable of being wet-etched, easy to handle with, and excellent in crystallinity can be used as a material for an active layer or a cladding layer of a semiconductor light emitting device such as a blue light emitting diode or a blue laser diode in which an active layer is sandwiched between cladding layers, so that a blue semiconductor light emitting device being excellent in light emission characteristics can be obtained.