A semiconductor device includes at least one nanowire that is disposed over a substrate, extends to be spaced apart from the substrate, and includes a channel region, a gate that surrounds at least a part of the channel region, and a gate dielectric film that is disposed between the channel region and the gate. A source/drain region that contacts one end of the at least one nanowire is formed in a semiconductor layer that extends from the substrate to the one end of the at least one nanowire. Insulating spacers are formed between the substrate and the at least one nanowire. The insulating spacers are disposed between the gate and the source/drain region and are formed of a material that is different from a material of the gate dielectric film.