The valance band structure of metalorganic vapor phase epitaxy (MOVPE) grown strained GaxIn1−xAs/InP single quantum well structures is experimentally verified by the determination of the effective in‐plane hole masses. The masses are obtained by performing magnetotransport experiments. Mobilities up to 8700 cm2/V s for gallium content ofx=0.3 were reached. The effective heavy hole masses of compressively strained GaInAs are drastically reduced compared to bulk material in excellent agreement to calculations using thek⋅p‐perturbation theory, whereas the masses of the uppermost valence band of tensile strained material appear to be rather high. Consequently, no experimental determination was possible in the latter case. A precise analysis of the Shubnikov–de Haas oscillation patterns of compressively strained quantum wells shows a spin splitting of the uppermost heavy hole band, containing two different effective masses. ©1995 American Institute of Physics.