Method of fabrication of a semiconductor device including at least the implementation of the following steps: - fabrication, on a substrate , of at least one stack comprising at least one alternating formed of a first portion of a first semiconductor between two second portions of a second semiconductor which is different from the first semiconductor and capable of being selectively etched relative to the first semiconductor, such that the thickness of at least the first portion is substantially equal to the thickness of nanostructures intended to be made; - fabrication, on a part of the stack , of external spacers and of at least one dummy gate arranged between the external spacers , - etching of the stack such that remaining parts of the first and second portions are only arranged beneath the dummy gate and beneath the external spacers and form a stack of nanowires, - thermal treatment of the stack at a temperature which causes at least one migration of atoms of the second semiconductor of free surfaces of remaining parts of the second portions towards free surfaces of at least one remaining part of said at least one first portion , corresponding to extremities of said at least one remaining part of said at least one first portion and at which nanostructures comprising at least atoms of the second semiconductor, - fabrication of source and drain regions by epitaxy of semiconductor from at least the nanostructures , and such that the second semiconductor is capable of being selectively etched relative to the semiconductor of the source and drain regions , - removal of the dummy gate and of the remaining part of the second portion , - fabrication of a gate between the external spacers and surrounding at least one channel of the semiconductor device formed by said at least one remaining part of said at least one first portion . - fabrication, on a substrate , of at least one stack comprising at least one alternating formed of a first portion of a first semiconductor between two second portions of a second semiconductor which is different from the first semiconductor and capable of being selectively etched relative to the first semiconductor, such that the thickness of at least the first portion is substantially equal to the thickness of nanostructures intended to be made; - fabrication, on a part of the stack , of external spacers and of at least one dummy gate arranged between the external spacers , - etching of the stack such that remaining parts of the first and second portions are only arranged beneath the dummy gate and beneath the external spacers and form a stack of nanowires, - thermal treatment of the stack at a temperature which causes at least one migration of atoms of the second semiconductor of free surfaces of remaining parts of the second portions towards free surfaces of at least one remaining part of said at least one first portion , corresponding to extremities of said at least one remaining part of said at least one first portion and at which nanostructures comprising at least atoms of the second semiconductor, - fabrication of source and drain regions by epitaxy of semiconductor from at least the nanostructures , and such that the second semiconductor is capable of being selectively etched relative to the semiconductor of the source and drain regions , - removal of the dummy gate and of the remaining part of the second portion , - fabrication of a gate between the external spacers and surrounding at least one channel of the semiconductor device formed by said at least one remaining part of said at least one first portion . <EOS>