STEM education is essential for preparing students for the digital age, fostering critical thinking, problem-solving, and technological literacy. Despite increasing recognition of its importance, challenges persist in effectively selecting and implementing STEM activities. Educators often lack a structured framework to align STEM lessons with student needs, available resources, and pedagogical objectives. In response, we propose EduPKG, an educational ontology designed to streamline STEM activity planning. EduPKG serves as a decision-making tool, enabling educators to select and customize activities that are engaging, feasible, and aligned with learning outcomes. By structuring STEM education around competencies such as problem-solving, creativity, collaboration, and critical thinking, EduPKG enhances lesson planning while ensuring adaptability to diverse educational settings. EduPKG was validated by conducting surveys with experts and analyzing a what-if scenario.