The selective area epitaxy of GaInAs/InP layers grown by low‐pressure metalorganic vapor phase epitaxy through SiO2patterned masks was investigated. The layers are found to develop mesa structures limited by {111} and (100) facets outside of the opened mask, and perfect selective epitaxy is obtained. The absence of GaInAs growth on {111} facets allows the fabrication of very narrow buried GaInAs layers in a single growth step. For both materials, the growth rates are found to depend strongly on the mask geometry owing to surface diffusion of the reactant species from the no‐ or low‐growth SiO2mask and {111} facets toward (100) surfaces. A detailed quantitative analysis is made to identify the critical parameters that control the growth behavior, and a model is described from which the upper limit of the growth rates for any mask design can be calculated. Low‐temperature cathodoluminescence measurements show strong emission of the buried GaxIn1−xAs layers and indicate local stoichiometry variations &Dgr;x&bartil;±5% around thex=47% lattice‐matched composition that are attributed to different diffusion coefficients of the reactant species on the SiO2mask and {111} facets. The results show that selective area metalorganic vapor phase epitaxy is a promising technique for the fabrication of one‐step‐grown buried quantum‐well wire arrays and narrow cavity InP‐based buried lasers.