We have carried out a Shubnikov-de Haas (SdH) measurement at 4 K and investigated the electronic properties and scattering mechanisms in a pseudomorphic In0.7Ga0.3As/In0.52Al0.48As quantum well high electron mobility transistor QW-HEMT) structure with a thin spacer thickness of 3 nm grown on a (411)A-oriented InP substrate by molecular-beam epitaxy (MBE). Electrons occupied the zeroth and first subbands in the 12-nm-thick In0.7Ga0.3As channel layer at two-dimensional electron gas (2DEG) densities of 3.10 X 10(12) and 0.99 X 10(12) cm(-2), respectively. 2DEG mobilities of the (411)A sample for the zeroth and first subbands were mu (0) = 52 000 and mu (1) = 66 000 cm(2)/V s, which were much higher than those of the (100) QW-HEMT structure (mu (0) = 22000 and mu (1) = 26000 cm(2)/Vs). The result indicates that the electron mobility of the (411)A sample is enhanced by reduction of remote impurity scattering because the spacer thickness (L-sp = 3 nm) and distribution of sheet doped impurities are laterally uniform in the (411)A In0.7Ga0.3As/In0.52Al0.48As QW-HEMT structure.