Much enhanced electron mobility of 105 000cm2∕Vs with a high sheet electron concentration (Ns) of 3.1×1012cm−12 was obtained at 77K in pseudomorphic In0.74Ga0.26As∕In0.46Al0.54As modulation-doped quantum well (MD-QW) grown on a (411)A InP substrate by molecular-beam epitaxy. This MD-QW has the “(411)A super-flat interfaces” (effectively atomically flat interfaces over a wafer-size area), which leads to significant reduction of interface roughness scattering at low temperatures. The highest electron mobility of the (411)A MD-QW was achieved by using pseudomorphic In0.46Al0.54As barriers. The electron mobility is 44% higher than that (73 000cm2∕Vsat77K) of a similar MD-QW structure grown on a conventional (100)InP substrate.