Power hybrids are particularly well suited for application in transportation systems because they combine a high level of functionality with low weight, size, and cost in a single electronic package. They are easy to interface with the system's logic, minimize electrical resistance and voltage overshoots, often incorporate protective circuits, allow easy fault detection and replacement, and can be largely technology transparent. An example of such a power hybrid package suitable for automotive applications was recently developed by GE and has been given the MO-55 designation by JEDEC.The power hybrid is discussed in terms of package electrical resistance, thermal resistance, both transient and steady state, and reliability, particularly corrosion protection and solder fatigue. Modeling, including finite element analysis, is applied to analyze heat flow and thermal interactions. In particular, the effect of various heatsinking and heatspreading approaches is given. Thus, the problem of choosing a heatspreader can be reduced to a simple tradeoff between chip area, the heatspreader thickness, and the heat transfer coefficient to the heat-sink. Generalized curves allow an easy assessment of heatsinking options.Highly Accelerated Stress Testing (HAST) allows a rapid assessment of corrosion resistance of the power hybrid construction approach toward damp heat under electrical bias. The thin aluminum metallization on the semiconductor chips and the bond wires are particularly vulnerable. Finally, solder fatigue is also strongly influence by the environmental conditions.