In this letter we report on the use of selective metalorganic vapor phase epitaxy growth as an original tool to alleviate the problem of random formation of microcracks in thick GaAs‐on‐Si heteroepitaxial layers. Through the use of a special mask design including the definition of sharp wedges in the SiO2mask material, the thermally induced stress in the GaAs‐on‐Si layers preferentially relaxes at precisely located sites on the substrate. The influence of mask configuration, wedge shape, wedge orientation, and layer thickness on microcrack formation has been investigated. Results obtained show that small‐area SiO2wedges are useful for the definition of microcrack location, and thus eventually for optoelectronic device processing.