MBE growth of epitaxial layers on selected areas of a growth surface (e.g., wafer or epi-layer grown thereon) is achieved by masking portions of the surface with an amorphous material and directing molecular beams at the masked surface so that a polycrystalline layer deposits on the mask and an epi-layer grows in the unmasked zones. The mask material is then exposed to a suitable etchant effective to dissolve that material, lift-off the polycrystalline layer and expose the underlying surface. Self-aligned contacts can be fabricated by depositing a metal layer prior to etching. Subsequent lift-off removes both the polycrystalline layer and the overlying metal. This process can be utilized in the fabrication of FETs and opto-electronic devices such as double heterostructure junction lasers.