We have calculated the concentrationnsoof the two‐dimensional gas in the AlGaAs/GaAs modulation‐doped structures with graded heterointerfaces. Our calculation shows thatnsoincreases with the increase in the grading lengthWGRat small values ofWGR. Depending on composition and doping of the AlGaAs layer the maximum value ofnsois achieved forWGRbetween 20 and 70 A˚. An increase in the concentration of the 2‐d gas leads to a larger device transconductance and to a large current swing. Hence, the device performance may be improved by grading the heterointerface.