A semiconductor device according to an embodiment includes a first region including an oxide semiconductor containing indium (In), gallium (Ga), and zinc (Zn), a second region and a third region between which the first region is disposed, at least one of the second region and the third region having a higher indium (In) concentration than the first region and containing at least one metal element from the group consisting of titanium (Ti), tungsten (W), copper (Cu), zinc (Zn), aluminum (Al), lead (Pb), and tin (Sn), an electrode; and an insulating layer disposed between the first region and the electrode.