This paper examines the shift toward an economic-security and national-strategy nexus in international relations through the case of South Korea's semiconductor industry in the age of artificial intelligence. It develops the concept of techno-economic statecraft to explain how states convert technology, supply chains, market access, and institutional rules into strategic leverage. Using process tracing and a qualitative single-case analysis informed by weaponized interdependence, informal economic sanctions, economic statecraft, and strategic hedging, the paper follows the sequence from structural vulnerability in the THAAD dispute and Japan's export controls to AI-driven HBM demand, U.S.–China technology competition, South Korea's industrial-diplomatic response, and China's counter-response. It argues that South Korea attempts to transform structural dependence into strategic indispensability through industrial upgrading, domestic institutional support, alliance management, and multilateral cooperation. Building a three‑layer analytical framework combining structural network conditions, state instrumental capacity and middle‑power behavioural posture, the paper further distinguishes techno‑economic statecraft from related concepts to clarify its unique causal conversion logic. The findings suggest that middle‑power conditional autonomy is not equivalent to neutrality, but hinges on the effective utilisation of irreplaceable supply‑chain nodes amid great‑power rivalry. The case shows that global technology networks provide great powers with chokepoint power, but also that middle powers can preserve limited and conditional autonomy when they occupy indispensable nodes in critical supply chains.