We report an enhancement-mode InAlN/GaN MISHEMT with a low gate leakage current by a thermal oxidation technique under gate.The off-state source-drain current density is as low as～10~(17) A/mm at V_(GS)= 0 V and V_(DS) = 5 V.The threshold voltage is measured to be +0.8 V by linear extrapolation from the transfer characteristics.The E-mode device exhibits a peak transconductance of 179 mS/mm at a gate bias of 3.4 V.A low reverse gate leakage current density of 4.9×10~(17) A/mm is measured at V_(GS) =-15 V. We report an enhancement-mode InAlN / GaN MISHEMT with a low gate leakage current by a thermal oxidation technique under gate. The off-state source-drain current density is as low as ~10 ~ (17) A / mm at V_ (GS ) = 0 V and V DS = 5 V. The threshold voltage is measured to be +0.8 V by linear extrapolation from the transfer characteristics. The E-mode device exhibits a peak transconductance of 179 mS / mm at a gate bias of 3.4 VA low reverse gate leakage current density of 4.9 × 10 ~ (17) A / mm is measured at V GS = -15 V.