Semiconductor device and semiconductor memory device

A semiconductor device of embodiments includes: a first electrode; a second electrode; an oxide semiconductor layer provided between the first electrode and the second electrode and including a first region, a second region, and a third region between the first region and the second region; a gate electrode facing the third region; a first insulating layer facing the first region; a second insulating layer facing the second region; and a gate insulating layer between the gate electrode and the oxide semiconductor layer, containing oxygen (O) and at least one metal element selected from a group consisting of Al, Hf, Zr, La, Y, Zn, In, Sn, and Ga, and having a chemical composition different from that of the oxide semiconductor layer.