This paper suggests a generalized semi-Markov model for manpower planning, which could be adopted in cases of unavailability of candidates with the desired qualifications/experience, as well as in cases where an organization provides training opportunities to its personnel. In this context, we incorporate training classes into the framework of a non-homogeneous semi-Markov system and we introduce an additional, external semi-Markov system providing the former with potential recruits. For the model above, referred to as the Augmented Semi-Markov System, we derive the equations that reflect the expected number of persons in each grade and we also investigate its limiting population structure. An illustrative example is provided. Copyright © 2010 John Wiley & Sons, Ltd.