We have measured the high‐field transport characteristics of pseudomorphic InAsxP1−x/InP (0.3≤x≤1.0) modulation doped heterostructures at 300 and 77 K. The field dependent steady state average velocities increase steadily with increase inx. The maximum velocities that have been measured in InAs/InP are 1.7×107cm/s (2.5 kV/cm) and 3.2×107cm/s (2.2 kV/cm) at 300 and 77 K, respectively. These are the highest velocities measured in any modulation doped heterostructure. The field dependent channel carrier concentration and mobility data indicate that there is very little real space transfer of carriers at high fields and this is confirmed by results from steady state Monte Carlo calculations.