The current study explored the conceptualization of domain specificity of language mindset in the speaking domain. The purposes were to determine the level of foreign language speaking mindset among Thai undergraduate students, validate the psychological constructs related to foreign language speaking mindset, and identify the factors associated with foreign language speaking mindset among Thai undergraduate students. A survey on foreign language speaking mindset was developed, validated, and used in the present study. The results suggested that Thai undergraduate students adopted a moderate foreign language speaking mindset. Factor analysis suggested three factors associated with the foreign language speaking mindset: emotional outcomes of attribution, motivational process-oriented goals, and proactive responses in failure situations. Validation of the Foreign Language Speaking Mindset Inventory (FLSMI) demonstrated that this instrument is reliable and practical for measuring the foreign language speaking mindset of Thai undergraduate students. These results underscore the importance of a supportive learning environment, emphasizing the role of educators in providing constructive feedback and cultivating a growth mindset to enhance students' proactive learning strategies for foreign language speaking.