The security alliance between the United States and South Korea, once focused primarily on military defense, is evolving to include economic security and technological cooperation. The evolving partnership between the two countries, particularly in the areas of semiconductor supply chains and advanced technologies, features the deepening and broadening of the alliance in the form of a Global Comprehensive Strategic Alliance. This change is driven by intensifying competition between the United States and China, which has led to the securitization of key technologies like semiconductors. This paper examines the opportunities and challenges in deepening and broadening US-South Korea cooperation on semiconductor supply chains. While such developments support the shared objectives of advancing technological innovation, bolstering supply chain resilience, and addressing potential threats from China, challenges remain in diverging threat perceptions and concerns about collective deterrence. The study concludes that aligning strategic objectives in economic security and technological cooperation is essential to ensure the sustainability of the alliance and its ability to navigate the complex global techno-geopolitical landscape.