A method of efficiently forming a circuit using a thin film transistor with a semiconductor layer in which preferable crystallinity is obtained is provided. A location on which stress concentrates according to crystallization of a semiconductor layer formed on a substrate having unevenness corresponds to the edges and their vicinities of the unevenness provided on the substrate, that is, the boundary between a concave portion and a convex portion and its vicinities. Thus, the location in which stress concentration is caused can be specified and controlled according to the shape of a slit-shaped base layer. In addition, an island-like semiconductor layer (1305) which becomes the active layer of a TFT is formed on the concave portion or the convex portion of the substrate having the unevenness. At this time, at least a portion which becomes the channel formation region of the TFT is formed without crossing the boundary between the concave portion and the convex portion. Such TFTs are used in parallel to construct a TFT having a large channel width so that fluctuation in electrical characteristics is averaged.