Abstract: This paper proposes a method for the limit stress assessment of 100 V hybrid DC/DC converter in the space applications, to confirm the reliability requirement of the components. With a new typical product as an example, according to the key parameters for the model application, the related limit criteria and the first draft of the detailed device specifications, we formulate the limit stress assessment test items, the methods and the conditions, and carry out the targeted limit tests for the electrical stress, the temperature stress, and the mechanical stress. The test results include the various limits, the reliability margin and other information of the device, serving as a reference for the development and the application of 100 V hybrid DC/DC converter in space applications.