We demonstrate gate-all-around (GAA) multi-bridge channel FETs (MBCFETs) with sub-20 nm nanosheet thickness fabricated through an S/D regrowth process. Working devices with three-level stacked In0.53Ga0.47As nanosheets as thin as 15 nm have been fabricated using selectively regrown n+ In0.53Ga0.47As contact formation and a combination of precision dry etching and selective wet etching for In0.52Al0.48As sacrificial layers against In0.53Ga0.47As nanosheets. The devices also feature a high-k HfO2 and TiN metal gate by ALD in a cross-coupled manner, surrounding the three-level stacked In0.53Ga0.47As nanosheets. MBCFETs with Lg = 130 nm, WNS = 300 nm and tNS = 15 nm exhibit a record combination of ION = 2.2 mA/µm and gm_max = 5.7 mS/µm at VDS = 0.8 V, making efficient use of each multi-bridge channel along the S/D and gate width directions.