Abstract: A method for forming retrograde semiconductor substrate channel impurities profile of a semiconductor device by using phosphorus ions implantation, includes the steps of forming a sacrificial oxide layer on a semiconductor substrate, ion-implanting boron ions to adjust threshold voltage of the device, removing the sacrificial oxide layer, forming a gate oxide layer on the semiconductor substrate, depositing a gate polysilicon layer on the gate oxide layer, forming a gate by etching the gate polysilicon layer, ion-implanting firstly by implanting phosphorus ions to form lightly doped drain regions, and ion-implanting secondly by implanting phosphorus ions into the semiconductor substrate channel to form retrograde channel impurities profile as well as to achieve proper threshold voltage.