Doping impurity atoms into semiconductor materials changes the resistance of the material. Selecting the atomic species of a dopant and the precise control of the number of dopant atoms in a unit volume can control the resistance to a desired value. The number of dopant atoms is usually controlled when the materials are synthesized. It can also be controlled after synthesizing by injecting dopant atoms using an ion implantation technique. This physical method has now enabled atom by atom implantation at the desired position. Here, we propose an additional technique, based on the electrochemical potential of dopant atoms in a material. The technique enables the dynamic control of the number of dopant atoms through the application of bias to the material. We demonstrate the controlled removal of dopant atoms using Ag2+δS and Ag-doped Ta2O5 as model materials. The change in resistance accompanying the removal of dopant atoms is also observed.