In this paper, we have fabricated and characterized In0.7Ga0.3As quantum-well (QW) MOSFETs with bi-layer Al2O3/HfO2 gate stack, grown by ALD. The fabricated device with Lg = 4 µm exhibits excellent maximum transconductance (gm_max) in excess of 0.5 mS/µm, together with reasonably good electrostatics integrity, such as DIBL < 45 mV/dec and subthreshold swing < 110 mV/dec. In addition, we have modeled a trend of gm_max as a function of Lg, and benchmarked gm characteristics of our InGaAs MOSFETs against other reports, revealing that the value of gm demonstrated in this work is the highest among any other devices with similar values of Lg. In trying to understand how such performance comes from, we have extracted effective mobility, where the mobility in our devices is as high as 6,600 cm2/V-s at 300 K.