The effect of structural parameters on the transport characteristics from 15 to 300 K of molecular beam epitaxy-grown InGaAs/InAlAs two dimensional electron gas structures lattice-matched to InP is determined. The InAlAs buffer layer thickness was varied from 1000 to 10,000Å. One sample also incorporated a InGaAs/InAlAs superlattice. The buffer layer thickness and structure had almost no effect on the mobility or sheet density. The InAlAs spacer layer was varied from 25 to 200Å. Increases in the InAlAs spacer thickness resulted in a monotonically decreasing sheet density and a peak in the mobility versus spacer thickness at 100Å. The highest 77 K mobility was 66,700 cm2/V/sds with ND=1.2×1012 cm-2. The effect of illumination and temperature on the sheet concentration in these structures as well as on "bulk" InAlAs:Si was much smaller than in AlxGa1-xAs/GaAs structures or "bulk" AlxGa1-xAs, for x≅0.30, indicating that devices based on this material system will not be characterized by many of the device instabilities observed in the AlGaAs/GaAs system. © 1991 The Minerals, Metals & Materials Society.