Investigation of the post-growth technique for fabricating multijunction solar sells based on the GaInP/GaAs/Ge heterostructure has been carried out. Investigated were methods of liquid chemical and electro-chemical etching of heterostructure layers. Technology for creating the separation mesa-structure has been developed. The improvement of the surface quality and of the profile of the mesa lateral side for heterostructures of different layer content has been achieved.