An in-situ gettering method for removing impurities from the surface and interior of a upgraded metallurgical grade silicon wafer is continuously conducted in a reaction chamber. Chloride gas is mixed with carrier gas. The gaseous mixture is used to clean the surface of the silicon wafer. Then, the gaseous mixture is used to form a porous structure on the surface of the silicon wafer before hot annealing is executed. Finally, the gaseous mixture is used to execute hot etching on the surface of the silicon wafer and remove the porous structure from the surface of the silicon wafer. As the chloride gas is used to clean the surface of the silicon wafer and form the porous structure on the surface of the silicon wafer, external gettering is improved. Moreover, interstitial-type metal impurities are effectively removed from the interior of the silicon wafer.