Periodic arrays of 150 and 175 nm‐wide GaAs–AlAs quantum wires and quantum dots were investigated, fabricated by electron beam lithography, and SiCl4/O2reactive ion etching, by means of reciprocal space mapping using triple axis x‐ray diffractometry. From the x‐ray data the lateral periodicity of wires and dots, and the etch depth are extracted. The reciprocal space maps reveal that after the fabrication process the lattice constant along the growth direction slightly increases for the wires and even more so for the dots. ©1995 American Institute of Physics.