A semiconductor device is provided. The semiconductor device includes a first semiconductor layer; a second semiconductor layer on the first semiconductor layer; an active region between the second semiconductor layer and the first semiconductor layer; an electron blocking structure between the active region and the second semiconductor layer; a first nitride semiconductor layer between the active region and the electron blocking structure; and a second nitride semiconductor layer between the electron blocking structure and the second semiconductor layer. The first nitride semiconductor layer includes a first indium content, a first aluminum content and a first conductivity-type dopant. The second nitride semiconductor layer includes a second indium content, a second aluminum content and a second conductivity-type dopant. The electron blocking structure includes a first semiconductor layer including a third indium content and a third aluminum content; wherein the third indium content is greater than the second indium content.