The online detection of aging bond wires is key to the health status awareness of smart power converters. In this paper, a new health precursor of the gate voltage undershoot VGE(pk) of the complementary switch in the half-bridge structure is proposed. It can be used to identify and distinguish multi-site bonding wire failures for both insulated gate bipolar transistors (IGBTs) and freewheeling diodes (FWDs) in multichip IGBT modules. A theoretical analysis is conducted to derive this novel precursor, which is then verified by experimental results. Then, a dedicated read-out circuit is designed for the data acquisition front end that can be integrated into gate drivers for in-situ monitoring. Finally, the effectiveness of this method is evaluated under changing operating conditions including the DC-bus voltage, the load current, and the junction temperature. The effects of their fluctuations are studied and quantified, with corresponding calibration relationships provided to improve precursor accuracy.Index Terms-Bond wire diagnosis, crosstalk phenomenon, freewheeling diode (FWD), insulated gate bipolar transistor (IGBT).