An extensive 3-D conjugate numerical study is conducted to assess the thermal performance of the novel Power Quad Flat No Lead (PQFN) packages for automotive applications. Several PQFN packages are investigated, ranging from smaller die/flag size to larger ones, single or multiple heat sources, operating under various powering and boundary conditions. The steady state and transient thermal performance are compared to those of the classical packages, and the impact of the thicker lead frame and die attach material on the overall thermal behavior is also evaluated. Under one steady state (1W) operating scenario, the PQFN package reaches a peak temperature of ~106.3°C, while under 37W@40ms of transient powering, the peak temperature reached by the corner FET is ~260.8°C. With an isothermal boundary (85°C) attached to the board backside, the junction temperature does not change, as the PCB has no significant thermal impact. However, when the isothermal boundary is attached to package bottom, it leads to a drop in by almost 20% after 40 ms. Additional transient cases are evaluated, with an emphasis on the superior thermal performance of this new class of power packages for automotive applications.