Semiconductor device having nickel silicide layer

A method for manufacturing a semiconductor device includes: forming an isolation region for defining a plurality of active regions in a silicon substrate; doping p-type impurities in at least one of the plurality of active regions to form a p-type well; forming an NMOS gate electrode traversing the p-type well via a gate insulating film; implanting n-type impurity ions into the p-type well on both sides of the NMOS gate electrode to form n-type extension regions; forming an NMOS gate side wall spacer on side walls of the NMOS gate electrode; implanting n-type impurity ions into the p-type well outside the NMOS gate side wall spacers to form n-type source/drain regions; forming a nickel silicide layer in surface regions of the n-type source/drain regions; and implanting Al ions the said n-type source/drain regions to dope Al in the nickel silicide layer surface regions.