The formation of a denuded zone which is a defect-free region denuded of crystal defects and metallic impurities is studied. Experimentally observed results are compared with the results calculated by a simulation program. In calculating the depth of the denuded zone, a new criterion of P=1/2 $P_{\mbox{bulk}}$ is proposed, which renders the experimental and simulation results agree with each other. The effects of internal gettering on device performances are also investigated in terms of the gate oxide rupture voltage, p-n diode reverse leakage current, etc. It has been proven that internal gettering improves device performances considerably.