In this work, we study the molecular beam epitaxial growth of strained InGaAs alloys on InP in order to increase as far as possible the In content of the active layer of heterostructures. We show that a reduction of the growth temperature with respect to the 500 ° C usual one could be efficient to increase the critical thickness for strain relaxation but does not result in an electron mobility improvement. At 500° C, the maximum In content compatible with an active layer thickness of 10-15 nm is 0.75. Within this framework, the electron mobility rises to 16 000 and 139 000 cm(2)/V s at 300 and 77 K, respectively, for a heterostructure with a 140 &ANGS; thick channel layer and a 400 &ANGS; thick spacer layer. Both values are among the best ones ever reported for a InGaAs/InAlAs heterostructure. © 2005 Elsevier B.V. All rights reserved.