According to an embodiment, a semiconductor device includes a first layer including a first nitride semiconductor, a second layer provided on the first layer and including a second nitride semiconductor having a wider bandgap than the first nitride semiconductor. The device also includes a source electrode and a drain electrode provided on the second layer; and a gate electrode provided on the second layer and located between the source electrode and the drain electrode. The second layer includes a first region between the gate electrode and the drain electrode, the first region being selectively provided in a surface of the second layer and contains fluorine. A concentration of fluorine in the first region is higher than a concentration of fluorine in a portion underneath the gate electrode in the second layer.