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Speaking is not a compulsory language skill assessed in the English subject of the National College Entrance Examination in China. This explains why, in elementary and secondary schools, less focus has been placed on the development of English-speaking abilities among Chinese students, resulting in their unbalanced mastery of language skills. Although self-efficacy is a crucial factor influencing students’ language performance, our understanding of speaking self-efficacy is insufficient in terms of its construct, its sources, and the relationships between the two. We, therefore, constructed psychometrically sound instruments to measure speaking self-efficacy, including the EFL Speaking Self-Efficacy Scale (EFL-SSES) and the EFL Sources of Speaking Self-Efficacy Scale (EFL-SSSES), in accordance with Bandura’s 1986 self-efficacy theory. Additionally, we performed path analysis to figure out the relationship between the construct and the sources of speaking self-efficacy. The results revealed the key role of physiological and emotional states and marginal importance of vicarious experience for speaking self-efficacy, advancing our grasp of self-efficacy theory in the speaking domain. Our research sheds valuable light on how to assist researchers and educators in identifying and enhancing students’ speaking self-efficacy via a variety of sources.