A semiconductor device with favorable electrical characteristics is provided. A semiconductor device with stable electrical characteristics is provided. A highly reliable display device is provided. The semiconductor device includes a first conductive layer, a first insulating layer, a semiconductor layer, and a pair of second conductive layers. The first insulating layer is in contact with a top surface of the first conductive layer. The semiconductor layer is in contact with a top surface of the first insulating layer. The pair of second conductive layers are in contact with a top surface of the semiconductor layer. The pair of second conductive layers are apart from each other in a region overlapping with the first conductive layer. The semiconductor layer contains indium and oxygen and has a composition falling within a range obtained by connecting first coordinates (1:0:0), second coordinates (2:1:0), third coordinates (14:7:1), fourth coordinates (7:2:2), fifth coordinates (14:4:21), sixth coordinates (2:0:3), and the first coordinates in this order with a straight line in a ternary diagram showing atomic ratios of indium to an element M and zinc. In addition, the element M is one or more of gallium, aluminum, yttrium, and tin.