This paper reports a simple I-V method for the first time to determine the lateral lightly-doped source/drain (S/D) profiles (n region) of LDD n-MOSFET's. One interesting result is the direct observation of the reverse-short-channel effect (RSCE) . It is observed that S/D n- doping profile is channel length dependent if reverse short-channel effect exists as a result of the interstitial imperfections caused by Oxide Enhanced Diffusion (OED) or S/D implant. Not only the lateral profiles for long-channel devices but also for short-channel devices can be determined. One other practical application of the present method for device drain engineering has been demonstrated with a LATID MOS device drain engineering work. It is convincible that the proposed method is well suited for the characterization and optimization of submicron and deep-submicron MOSFET's in the current ULSI technology.