There is provided a thin-film transistor that is formed on an insulating substrate, is capable of a high-speed operation, has small non-uniformity among devices, is hardly susceptible to device destruction due to high voltage, and is free from the effect of a parasitic transistor that forms at an edge part of an Si island. The thin-film semiconductor device is formed using a thin-film semiconductor provided on the insulating substrate and includes a gate region for formation of a channel region through which a drain current flows. The gate region has a ring shape in plan on the insulating substrate. High concentration impurity-doped regions are dividedly provided on an inside and an outside of the ring-shaped gate region, and the channel region is formed of a plurality of fan-shaped semiconductor single-crystal portions.
