A miniaturized transistor, a transistor with low parasitic capacitance, a transistor with high frequency characteristics, or a semiconductor device including the transistor is provided. The semiconductor device includes a first insulator, an oxide semiconductor over the first insulator, a first conductor and a second conductor that are in contact with the oxide semiconductor, a second insulator that is over the first and second conductors and has an opening reaching the oxide semiconductor, a third insulator over the oxide semiconductor and the second insulator, and a fourth conductor over the third insulator. The first conductor includes a first region and a second region. The second conductor includes a third region and a fourth region. The second region faces the third region with the first conductor and the first insulator interposed therebetween. The second region is thinner than the first region. The third region is thinner than the fourth region.