We have experimentally demonstrated fully suspended nanowire (NW) gate-all-around (GAA) negative-capacitance (NC) field-effect transistors (FETs) with ultrasmall channel dimensions (5-nm × 12.5 -nm); they exhibit a remarkable Ion-Ioff ratio of over 1010. This work, for the first time, experimentally studies and compares the structures of metal-ferroelectric-metal-insulator-semiconductor (MFMIS) and metal-ferroelectric-insulator-semiconductor (MFIS) NCFETs. The GAA with the MFMIS structure has a higher on-state current owing to the metallic equal-potential layer and superior S.S min of 39.22 mV/decade. A ZrO2 seed-layer is inserted under HfZr 1-x, Ox(HZO) to improve the ferroelectric crystallinity. Consequently, post-metal annealing (PMA), the conventional crystallization annealing step, can be omitted in the presence of o-phase. The gate current (IG) is monitored to verify the multi-domain HZO. A negative DIBL of -160 mV/V is observed because of the strong NC effect corresponding to previous simulated results.