We investigate the effects of hydrogen-based post-metallization annealing on InGaAs MOSFETs integrated on insulator on Si substrates. We find that several aspects of device performance are improved by post-metallization annealing. While a 325°C anneal offers maximum improvement of the subthreshold slope, a 300°C anneal yields the highest transconductance and lowest on-resistance. We correlate these improvements with a reduction of contact resistance as well as density of interface traps near the conduction band edge. Overall, by use of the high-temperature annealing scheme, the on-current at VDD = 0.5 V and IOFF = 100 nA/µm was improved by 66% compared to no annealing.