The morphology of porous layers obtained by electrochemical etching of (100) oriented n-GaAs substrate,, in ail aqueous solution of HCl was studied. At low anodic current densities, up to 5 mA/cm(2), pores in the form of triangular prisms grew along (111) crystallographic directions. For larger current densities the shape of the pore,, did not suffer any changes at the beginning of the process, while after a definite period of time the morphology of pores changed drastically to chains of tetrahedral voids with [111] facets.