Nitride semiconductor device

A nitride semiconductor device comprising:

• an n-region layer structure including a first n-region multi-film layer having at least one first nitride semiconductor film and at least one second nitride semiconductor film, said at least one second nitride semiconductor film having a same composition and a different concentration of n-type impurity than said at least one first nitride semiconductor film;
• a p-region layer structure;
• and
• an active layer, interposed between said n-region and said p-region layer structures, made of a quantum well structure comprising a well layer of InjGa1−jN (0≦j<1);
• wherein said n-region layer structure further includes a second n-region multi-film layer having at least one fifth nitride semiconductor film and at least one sixth nitride semiconductor film, said at least one sixth nitride semiconductor film having a different composition than said at least one fifth nitride semiconductor film, said second n-region multi-film layer being interposed between said first n-region multi-film layer and said active layer, said at least one fifth nitride semiconductor film containing In.