We have investigated the effects of the tri-gate channel structure on electrical properties of extremely thin-body (ETB) InAs-on-insulator (-OI) MOSFETs. It was found that the tri-gate structure provides significant improvement in short channel effect (SCE) control even in ETB-OI MOSFETs by the simulation. We have fabricated and demonstrated tri-gate InAsOI MOSFETs with fin width of the top surface down to 40 nm. The tri-gate ETB InAs-OI MOSFETs shows better SCEs control with small effective mobility (mu(eff)) reduction. Thus, we have demonstrated the operation of sub-20-nm-channel length (L-ch) InAs-OI MOSFETs. The 20-nm-L-ch InAs-OI MOSFETs show good electrostatic with subthreshold slope of 120 mV/decade and drain induced barrier lowering of 110 mV/V, and high transconductance (G(m)) of 1.64 mS/mu m. Furthermore, we have realized a wide-range threshold voltage (V-th) tunability in tri-gate InAs-OI MOSFETs through back bias voltage (V-B) control.