Silicon power devices are a major reliability concern for power electronics converters. Failure modes, mechanisms, and effects (FMMEA) is a well-established method for identifying and analyzing the critical failure mechanisms and improving the reliability of a system through the process. The effects of the various failure mechanisms (and modes) are system dependent and cannot be identified in isolation. This work establishes a Failure Modes and Mechanisms Analysis (FMMA) for silicon power devices that identifies the relevant failure modes and mechanisms for those components. Following the FMMA, a set of failure analysis case studies of silicon power devices which aid in the identification of failure causes and mechanisms for the FMMA are described. Finally, the criticality of the different mechanisms is discussed based on the severity of a failure within a given system, the occurrence of a failure mechanism for a given component, and the ability to detect a failure using techniques such as PHM, criticality can be identified for the mechanisms.