A method of manufacturing a semiconductor device characterized by its high-speed operation and high reliability is provided in which a semiconductor layer crystallized by a CW laser is used for an active layer of a TFT. When a semiconductor layer is crystallized by a CW laser, one part is formed of large crystal grains whereas another part is formed of microcrystals due to the width-wise energy density distribution. The former exhibits excellent electric characteristics. The latter has poor electric characteristics because grain boundaries hinder movement of electric charges, and therefore causes inconveniences when used as an active layer of a transistor. Accordingly, circuits are arranged such that a semiconductor layer formed of large crystal grains is used for the active layer of every TFT.