High‐performance Ga0.4In0.6As/Al0.55In0.45As pseudomorphic modulation‐doped field‐effect transistors (MODFET’s) have been further improved by replacing the Al0.48In0.52As buffer layer with an Al0.55In0.45As/Al0.41In0.59As strained‐layer superlattice (SLS) buffer layer, grown lattice matched to InP substrate by molecular‐beam epitaxy (MBE). Extrinsic transconductance as high as 306 mS/mm at 300 K has been obtained along with complete pinch off behavior for 1.7 μm gate length devices. This is attributed to the dislocation filtering and impurity gettering effects of the Al0.55In0.45As/Al0.41In0.59As SLS. Structural characterization using double crystal x‐ray diffraction also reveals the high quality of this SLS buffer layer.