A semiconductor device includes a first nitride semiconductor layer containing Ga, a second nitride semiconductor layer provided on the first nitride semiconductor layer containing Ga, a first electrode and a second electrode provided on or above the first nitride semiconductor layer and electrically connected to the first nitride semiconductor layer, a gate electrode provided between the first electrode and the second electrode, a conductive layer provided on or above the second electrode, of which a first distance to the second electrode is smaller than a second distance between the second electrode and the gate electrode, and which is electrically connected to the first electrode or the gate electrode, a first aluminum oxide layer provided between the gate electrode and the second electrode and provided between the second nitride semiconductor layer and the conductive layer, a silicon oxide layer, and a second aluminum oxide layer.