This study explores how the use of a surface-charge-based instructional approach affects introductory university level students' understanding of direct current (dc) circuits. The introduced teaching intervention includes electrostatics, surface-charge-based micro-models that explain the existence of an electric field inside the current-carrying wire, and traditional Kirchhoff's laws that are based on the conservation principles of energy and charge. The study group consisted of 32 students, 5 of whom were carefully monitored during the course. The results show that students' pre-knowledge includes various naive micro-models related to electric current. Students try to create connections between electrostatics and dc circuits by themselves without the concept of an electric field. During the intervention, the students abandoned naive models almost completely. In the final exam, approximately 30% of the students reached the level of desired understanding and 50% of the students reached an understanding that can be considered as a good basis for further studies. Generally, the introduced instructional approach can be recommended because it explains dc circuits holistically, based on conservation principles and offers digestible micro-level models. These matters help students to abandon their naive models. (Contains 3 tables and 6 figures.)