Method for making a semiconductor device, comprising: a) making of a stack of crystalline semiconductor layers comprising a first layer and a second layer capable of being selectively etched in relation to the first layer, b) etching of part of the stack, a portion of the first layer forms a nanowire (132) arranged on the second layer, c) selective etching of second layer, d) making, beneath the nanowire, of a sacrificial portion which has an etching selectivity which is greater than that of the second layer, e) making of a sacrificial gate and of an external spacer surrounding the sacrificial gate, f) etching of the stack, revealing ends of the nanowire and of the sacrificial portion aligned with the external spacer, g) selective etching of parts of the sacrificial portion, from its ends, forming aligned cavities beneath the external spacer, h) making of an internal spacer within the cavities.