A semiconductor device having favorable electrical characteristics can be provided. The semiconductor device having favorable electrical characteristics is provided. The semiconductor device has a structure including a first metal oxide layer including a first region, and a second region and a third region in which phosphorus, boron, aluminum, or magnesium is added and between which the first region is sandwiched; a conductive layer which overlaps with the first region; a first insulating layer which covers a side surface and a bottom surface of the conductive layer; a second metal oxide layer which covers a side surface and a bottom surface of the first insulating layer and is in contact with a top surface of the first region; a second insulating layer in contact with a top surface of the second region and a top surface of the third region and in contact with a side surface of the second metal oxide layer; a third insulating layer positioned over the second insulating layer and in contact with a side surface of the second metal oxide layer; a fourth insulating layer positioned over the third insulating layer and in contact with a side surface of the second metal oxide layer; a fifth insulating layer in contact with a top surface of the conductive layer, a top surface of the first insulating layer, a top surface of the second metal oxide layer, and a top surface of the fourth insulating layer.