A transistor with a small footprint is provided. A transistor having high reliability is provided. A transistor is provided over an insulating layer that has a projection. Over the projection, at least a channel formation region of a semiconductor layer is provided. This can reduce the footprint of the transistor. The transistor has a curved structure, which inhibits light that enters from the outside from reaching a channel formation region of the semiconductor layer. Accordingly, deterioration of the transistor due to external light can be reduced, whereby the transistor can have increased reliability. The projection can be obtained by utilizing the internal stress of the layer formed over the insulating layer. Alternatively, the projection can be obtained by placing, under the insulating layer, a structure body for providing the insulating layer with the projection.