Lattice deformations and misfit dislocations are studied by x‐ray double‐crystal diffraction and topography for GaInAsP/InP double‐heterostructure layers epitaxially grown on (001) InP substrates. No misfit dislocation was observed at the interfaces when the misfits &Dgr;a⊥/abetween the lattice constants normal to the wafer surface of GaInAsP (0.4 &mgr;m thick) and InP layers are within about 5×10−3. The unit cell of the GaInAsP epitaxial layer is tetragonally deformed due to the interface lattice misfit such that the lattice constant parallel to the wafer surface is nearly invariant across the GaInAsP/InP interfaces in the DH wafers both with and without misfit dislocations for ‖&Dgr;a⊥/a‖<6.4×10−3.