In machine learning the problem of limited data for supervised learning is a challenging problem with practical applications. We address a similar problem in the context of software quality modeling. Knowledge- based software engineering includes the use of quantitative software quality estimation models. Such models are trained using apriori software quality knowledge in the form of software metrics and defect data of previously developed software projects. However, various practical issues limit the availability of defect data for all modules in the training data. We present two solutions to the problem of software quality modeling when a limited number of training modules have known defect data. The proposed solutions are a semisupervised clustering with expert input scheme and a semisupervised classification approach with the expectation-maximization algorithm. Software measurement datasets obtained from multiple NASA software projects are used in our empirical investigation. The software quality knowledge learnt during the semisupervised learning processes provided good generalization performances for multiple test datasets. In addition, both solutions provided better predictions compared to a supervised learner trained on the initial labeled dataset.