This research was conducted to determine which source of self-efficacy is the most influential on the speaking performance of high-achiever students in terms of speaking skill. This research was carried out at the Department of English Language Education of UIN Ar-Raniry. This research used a descriptive qualitative approach. Research participants were selected using purposive sampling. The participants of this research were four English students from the 2019 batch. Furthermore, data was collected through semi-structured interviews. The research results showed the four sources of self-efficacy had a significant role in shaping students' performance in public speaking. However, psychological and affective states had the most dominant influence on students' self-efficacy in speaking skill. This was demonstrated by how students managed physical and emotional stress reactions well when performing public speaking tasks. Namely, students learned to control anxiety, nervousness, and even stress to show the best of what had been prepared and attempted as well as possible.