Activity theory is used to compare PhD undertaken at university, that is, academic PhD, with PhD performed in collaboration with industry, that is, semi-industrial PhD. The research is divided into a literature review and a case study. Semi-industrial and academic PhD are modelled as activity systems, and differences are highlighted in terms of subject, community, division of labour and instruments. Semi-industrial PhD involve interaction with people from a non-academic background, developing management skills. Furthermore, the supervision of semi-industrial PhD is more complex than that of academic PhD. If supported by frequent supervision, this complexity strengthens the PhD. If not, supervision becomes dispersive, and semi-industrial PhD students create a network of people that enables them to perform their research. However, the creation of that network is not systematic, and a lack of a network may affect the PhD research. Therefore, frequent supervision of semi-industrial PhD students should be stressed and structured.