A practical methodology for modeling the reliability of deep submicron (<90 nm) semiconductor microcircuits provides timely and needed information for the integration of commercial off the shelf (COTS) electronics in airborne and high reliability applications. Designing and assuring customer confidence in airborne high reliability applications becomes more challenging as electronics technologies develop rapidly and commercial application demands drive the increasing use of faster, more integrated, higher density commercial off the shelf (COTS) electronics. Use of COTS electronics provides advantages of greater computational power, with higher manufacturing volumes driving better quality control. COTS also introduce the new problem of life-limited semiconductors [1]. Outdated reliability assessment methods do not address these issues or adequately support reliable aerospace system design [2]. The Semiconductor Reliability project, launched in April 2013 by the Aerospace Vehicle Systems Institute (AVSI) under the Authority for Expenditure (AFE) 83, developed a practical approach to modeling the random and wearout failure mechanisms of deep sub-micron (<90 nm) microcircuits. Unlike prior physics of failure approaches, the methodology was kept simple and was implemented in a spreadsheet. This spreadsheet is provided free of charge to R&M practitioners to help promote understanding and common usage of the methodology. Recipients of the spreadsheet are expected to provide feedback to the AVSI team in return. The project also encourages microcircuit device suppliers to provide reliability information in some form, either by using the spreadsheet or directly providing the cumulative defect fraction (CDF) of their product in the application environments. When microcircuit device suppliers provide test data results for their products, the spreadsheet is used to scale the results from test to usage environments. The methodology developed by AVSI differs from traditional Arrhenius methods in that scaling is not only based on temperature but also on voltage, current and frequency. Models of time dependent dielectric breakdown (TDDB), hot carrier injection (HCI), negative bias temperature instability (NBTI) and electromigration (EM) are used to gain an accurate reliability assessment for technologies sensitive to these mechanisms. This paper describes the AVSI reliability research project, the semiconductor microcircuit reliability models, and provides examples of the applications of these models to support reliable avionics systems design.