A method of forming a GAA FinFET, including: forming a fin on a substrate, the substrate having a STI layer formed thereon and around a portion of a FIN-bottom portion of the fin, the fin having a dummy gate formed thereover, the dummy gate having a gate sidewall spacer on sidewalls thereof; forming a FIN-void and an under-FIN cavity in the STI layer; forming first spacers by filling the under-FIN cavity and FIN-void with a first fill; removing the dummy gate, thereby exposing both FIN-bottom and FIN-top portions of the fin underneath the gate; creating an open area underneath the exposed FIN-top by removing the exposed FIN-bottom; and forming a second spacer by filling the open area with a second fill; wherein a distance separates a top-most surface of the second spacer from a bottom-most surface of the FIN-top portion. A GAA FinFET formed by the method is also disclosed.