Students’ conceptual difficulties have been characterized in many fields of knowledge. However, the relevant research literature is limited in the case of analog and digital circuits. This gap should be addressed in light of the central role played by electronic circuits in electrical engineering and related disciplines. Therefore, the study aimed to identify undergraduate engineering students’ conceptual difficulties in analog and digital circuits. The study took place at two leading universities in Israel. Over 300 exams in electronic circuits (solved by undergraduate students) were analyzed. Based on this analysis, a list of core concepts in analog and digital circuits that caused conceptual difficulties was generated. In addition, a problem based on these concepts was created. Thirty electrical engineering students who completed introductory courses in electronic circuits were interviewed. In these think-aloud interviews, the students explained the above-mentioned concepts and solved the problem. The data underwent content analysis by two engineering education experts. According to the findings, students’ difficulties are mainly in the basic concepts of operating point, feedback and gain.