AbstractThe temperature dependence of the resistivity (ρ) of Ag-doped Bi₂Se₃ (Ag_xBi_2−xSe₃) shows insulating behavior above 35 K, but below 35 K, ρ suddenly decreases with decreasing temperature, in contrast to the metallic behavior for non-doped Bi₂Se₃ at 1.5–300 K. This significant change in transport properties from metallic behavior clearly shows that the Ag doping of Bi₂Se₃ can effectively tune the Fermi level downward. The Hall effect measurement shows that carrier is still electron in Ag_xBi_2−xSe₃ and the electron density changes with temperature to reasonably explain the transport properties. Furthermore, the positive gating of Ag_xBi_2−xSe₃ provides metallic behavior that is similar to that of non-doped Bi₂Se₃, indicating a successful upward tuning of the Fermi level.