New Ga0.47−u In0.53+uAs/Al0.48+uIn0.52−uAs pseudomorphic modulation-doped field-effect transistor (MODFET) heterostructures are proposed and grown by molecular-beam epitaxy on InP:Fe substrates. For heterostructures with u=0.07, Hall mobilities as high as 12 050, 59 970, and 87 300 cm2/V s at 300, 77, and 4.2 K, respectively, were measured. The corresponding sheet carrier densities in the dark were in excess of 1012 cm−2. No significant light sensitivity or persistent photoconductivity effects were observed. Shubnikov–de Haas oscillations confirmed the two dimensionality of the electron gas and indicated population of two electron subbands. Pseudomorphic MODFETs fabricated on such a heterostructure exhibit dc transconductances as high as 271 and 227 mS/mm at room temperature for 1.6 and 2.9 μm gate lengths, respectively. These results show that this material system is a strong candidate for the development of next generation high speed MODFETs that can be integrated with photonic devices.