High core-Vdd overvoltage latchup margins in CMOS ICs are required to enable many reliability screens (e.g., DVS and HTOL testing). We introduce an efficient way to isolate defects that degrade these margins using PEM and 1064/1340 nm CW laser-stimulation. Current pulses from a current amplifier are used to rapidly charge and discharge the DUT power rail to repetitively ramp Vdd to (or near) the latchup threshold. The characteristic drop in Vdd when latchup is induced is used to generate a latchup flag for laser-stimulation mapping. Latchup events are automatically terminated and latchup durations are minimized, leading to high stability/repeatability of the technique. Isolations down to the cell level were successfully performed in sub-14 nm FinFET test vehicles. This level of isolation is unmatched and this is the first reported use of thermal laser stimulation for latchup investigations. In one provided example, the latchup trigger was isolated to FET based decoupling capacitors (decaps) widely used as fill.