This paper puts forward a novel assessment framework, based on the Model of Domain Learning (MDL), to assess student development in various professional skills across Science, Technology, Engineering and Mathematics (STEM) disciplines. New graduates are not only required to have good technical skills but also excel in professional skills to be successful in their career choices. As a response, academic programs have integrated professional skills such as teamwork/communication, ethics, global awareness, creative problem solving, and leadership, into their curricula. However, there are challenges in the assessment of learning outcomes related to professional skills. By designing a uniform assessment framework for all professional skills and developing a set of coherent assessment instruments that can be tailored according to the learning objectives and student level, the proposed assessment framework aims to facilitate the integration of professional skills assessment into an overall program assessment plan. The proposed framework will be tested in various course levels (i.e., first year to senior) from STEM majors at various institutions.