A nanowire transistor according to the present invention includes: at least one nanowire 13 including a core portion 13a that functions as a channel region and an insulating shell portion 13b that covers the surface of the core portion 13a; source and drain electrodes 14 and 15, which are connected to the nanowire 13; and a gate electrode 21 for controlling conductivity in at least a part of the core portion 13a of the nanowire 13. The core portion 13a is made of semiconductor single crystals including Si and has a cross section with a curved profile on a plane that intersects with the longitudinal axis thereof. The insulating shell portion 13b is made of an insulator including Si and functions as at least a portion of a gate insulating film.