To provide a method for manufacturing an island-shaped semiconductor region having a forward taper side without a backward taper even when a semiconductor layer is thick.

A first semiconductor layer 11 is formed on an insulator, and a second semiconductor layer 16 in which the density of impurity is high is formed on the first semiconductor layer 11. Then, a mask 17 for regulating the semiconductor region of a thin film transistor is formed on the second semiconductor layer. Thereafter, a part uncovered with the mask of the first and second semiconductor layers is etched, and separated as an island-shaped semiconductor region in a first etching process; the mask is etched under the condition of the etching rate for the mask being made larger than the etching rate for the first and second semiconductor layers; the peripheral edge of each mask is shifted inside a second etching process; the part uncovered with the mask whose peripheral edge is shifted inside the first and second semiconductor layers is etched; and the shape of the island-shaped semiconductor region is corrected in a third etching process.