Auxiliary-source bond wires and connections are widely used in power modules with paralleled mosfets or insulated gate bipolar transistor (IGBTs). This paper investigates the operation mechanism of the auxiliary-source connections in multichip power modules. It reveals that the auxiliary-source connections cannot fully decouple the power loop and the gate loop such as the Kelvin-source connection, owing to their involvement in the loop of the power source current. Three effects of the auxiliary-source connections are then analyzed, which are 1) the common source stray inductance reduction, 2) the transient drain-source current imbalance mitigation, and 3) the influence on the steady-state current distribution. Finally, simulations and experimental results validate the theoretical analysis.