The structure of GaAs/AlGaAs quantum wires (QWRs) and vertical quantum wells (VQWs) grown by low‐pressure organometallic chemical vapor deposition was investigated by conventional and high resolution transmission electron microscopy, and by low‐temperature cathodoluminescence. The lower wire boundaries show a much smaller radius of curvature, as compared with atmospheric pressure growth of similar structures, and the upper boundaries show distinct faceting. More abrupt interfaces are obtained due to the kinetically limited growth, with measured interface grading as small as one or two monolayers. The VQW structures formed in the AlGaAs barrier exhibit several branches related to the faceting of the QWR boundaries. These characteristics of the low‐pressure nonplanar growth should allow the fabrication of quasi‐one‐dimensional QWRs with size and shape controlled on the monolayer level. ©1995 American Institute of Physics.