We describe here the properties of In0.53Ga0.47As/In0.52Al0.48As modulation‐doped heterostructures and field‐effect transistors grown directly by molecular‐beam epitaxy on GaAs substrates. The generation and nature of dislocations in the films have been studied by transmission‐electron microscopy. The final heterostructure contains a series of compositional steps of InxGa1-xAs (0≤x≤0.53) to generate and control the dislocation movement. The modulation‐doped heterostructures are characterized by μ300 K=8 150 cm2/V s (ns=2.7×1012 cm-2) and μ20 K=26 100 cm2/V s (ns=2.1×1012 cm-2) which compare very favorably with values measured in similar lattice‐matched heterostructures on InP. 1.4‐μm gate‐modulation‐doped field‐effect transistors exhibit gm(ext)=240 mS/mm and fT=21 GHz. The drain current variation with gate bias is linear and the transconductance is uniform over a sizeable voltage range. These material and device characteristics indicate that InxGa1-xAs/InxAl1-xAs transistors (with x varying over a certain range to vary ΔEc) can be designed on GaAs or even other mismatched substrates.