In a method of forming a gate-all-around field effect transistor (GAA FET), a fin structure is formed. The fin structure includes a plurality of stacked structures each comprising a dielectric layer, a CNT over the dielectric layer, a support layer over the CNT. A sacrificial gate structure is formed over the fin structure, an isolation insulating layer is formed, a source/drain opening is formed by patterning the isolation insulating layer, the support layer is removed from each of the plurality of stacked structures in the source/drain opening, and a source/drain contact layer is formed in the source/drain opening. The source/drain contact is formed such that the source/drain contact is in direct contact with only a part of the CNT and a part of the dielectric layer is disposed between the source/drain contact and the CNT.