The electronic parameters of a two-dimensional electron gas (2DEG) in unique modulation-doped InxGa1-xAs/InyAl1-yAs coupled step-rectangular quantum wells were investigated by using the Shubnikov–de Haas (SdH)–Van der Pauw Hall effect and cyclotron resonance measurements. The SdH measurements and the fast Fourier transformation results for the SdH data at 1.5 K indicated electron occupation of two subbands in the quantum well. The electron effective masses of the 2DEG were determined from the cyclotron resonance measurements, and their values qualitatively demonstrated the nonparabolicity effects of the conduction band on the 2DEGs in the quantum wells. The electronic subband energies, the energy wave functions, and the Fermi energies were calculated by using a self-consistent method taking into account exchange-correlation effects, together with strain and nonparabolicity effects. These results can help in understanding potential applications of unique InxGa1-xAs/InyAl1-yAs coupled step-rectangular quantum wells in high-speed electronic and long-wavelength optoelectronic devices. © 2003 American Institute of Physics.