A semiconductor device includes a first stacked portion above a substrate, the first stacked portion comprising a first nitride semiconductor layer containing aluminum and a second nitride semiconductor layer containing carbon, a third nitride semiconductor layer on the first stacked portion, the third nitride semiconductor layer containing carbon and having a greater thickness than each of the first and second nitride semiconductor layers, the third nitride semiconductor layer having a lower carbon concentration than the second nitride semiconductor layer, a second stacked portion on the third nitride semiconductor, the second stacked portion comprising a fourth nitride semiconductor layer containing aluminum and a fifth nitride semiconductor layer containing carbon, a sixth nitride semiconductor layer on the second stacked portion, a seventh nitride semiconductor layer on the sixth nitride semiconductor layer and containing aluminum, and a first electrode on the seventh nitride layer.