Abstract For the lattice mismatched epitaxy of InGaAs on GaAs, the use of the InAlAs intermediate layer grown by the two-step growth was studied. The InAlAs layers showed mirror-like surfaces, in spite of a large lattice mismatch of approximately 4%. It was suggested that the low temperature buffer layer relaxed the lattice mismatch and suppressed the three-dimensional growth. InGaAs layers were successfully grown on the InAlAs intermediate layers. The etch pit density revealed by molden KOH etching was (7−8)×107 cm−2 for the 1.2 μm thick InGaAs layer on InAlAs/GaAs. The electrons in InGaAs grown on InAlAs/GaAs were accumulated near the heterointerface between InGaAs and InAlAs, and an electron mobility of 5500 cm2/V·s was obtained with a sheet carrier density of 1.6×1012 cm−2.