To avoid latch-up failure in high voltage integrated circuits, a source-side engineering technique for on-chip ESD protection nLDMOS is proposed in this work. Experimental results have been verified in a 0.5-mum 16-V bipolar CMOS DMOS technology. Measurement results from transmission-line-pulsing system show that the proposed source-side engineering method can effectively increase the holding voltage of the nLDMOS from 10.5 V to 16.2 V. Transient-induced latch-up tests show that the proposed source-side engineering technique significantly improves the latch-up immunity of nLDMOS in on-chip ESD protection circuit.