A display device includes a display area composed of pixels in a matrix. Each pixel has a light-emitting element and a driving element to supply a driving current to the light-emitting element. The driving element includes a thin film transistor with a semiconductor layer of a poly-crystalline film. The semiconductor layer is provided with channel region, and a source and drain region disposed on both sides of the channel region. The channel region connects the source region to the drain region and has at least two conductive regions with different average grain sizes. The characteristics of the driving elements are made substantially uniform so that the display quality of the display device can be improved remarkably.