In a ZnO based compound semiconductor device, nitrogen (N) doped (Mg)ZnO:N layer is inserted as a diffusion barrier layer 9 between a ZnO based n-type layer 3 to which n-type dopants are doped and an active layer 4 or a p-type layer 5. The diffusion barrier layer 9 prevents diffusion of the n-type dopants to the active layer 4 or the p-type layer 5. Crystalline quality of the active layer 4 of the ZnO based compound semiconductor device is not deteriorated by the diffusion of the n-type dopants.