When p-type silicon is contacted to a noble metal in HF solution containing an oxidizing agent, a galvanic cell can be formed. The oxidizing agent is reduced at the metal and the semiconductor is etched. To achieve a similar effect with n-type silicon, illumination is required. On the other hand, a galvanic cell is formed with both n- and p-type silicons in alkaline solution in the dark. These results are explained on the basis of silicon electrochemistry with the use of energy band diagrams. It is shown that “galvanic etching” can be used to control the silicon surface morphology, e.g., to form microporous or macroporous layers or produce pyramid-free anisotropic structures.