The paper proposes a model for assessing the maturity of New Service Development (NSD) processes in manufacturing companies that offer product-services. The model adopts a five-stage scale, on which key elements are evaluated according to the following dimensions: 1) the approach used to manage processes and projects; 2) the use of specific resources, skills and tools; 3) the involvement of customers, suppliers and other stakeholders; 4) the adoption of performance management systems. An empirical application of the model was carried out, based on an inter-company workshop and in-depth interviews. Such a model is helpful in describing the maturity of NSD processes of a company, but also in identifying the main gaps and to prioritize the improvement actions.