A semiconductor foundry is a company that manufactures integrated circuits on behalf of fabless chip designers, providing fabrication services without designing its own products. Business model: foundries invest in fab construction ($15-30B+ for leading edge), process development, and manufacturing capability. Customers (fabless companies) provide chip designs; foundry fabricates and returns finished wafers. Major foundries: (1) TSMC—world's largest pure-play foundry (~60% market share), leading edge through 2nm; (2) Samsung Foundry—second largest, vertically integrated (also IDM); (3) GlobalFoundries—specializes in mature/specialty nodes after exiting leading-edge race; (4) UMC—mature nodes, cost-competitive; (5) SMIC—China's largest foundry. Foundry services: (1) Process technology—multiple nodes and variants (logic, RF, HV, BCD); (2) Design enablement—PDK, IP libraries, EDA tool qualification; (3) Multi-project wafer (MPW)—shared wafer for prototyping; (4) Mask making—in-house or contracted; (5) Wafer sort and packaging (OSAT partnerships). Revenue model: wafer pricing per process node (higher for advanced nodes), NRE charges for masks and setup, volume commitments. Capacity management: long-term agreements (LTAs) with major customers, capacity allocation decisions. Technology roadmap: foundries announce node timeline years ahead to attract design starts. Leading-edge economics: only TSMC, Samsung, Intel can afford $20B+ per fab for sub-5nm. Foundry model revolutionized the semiconductor industry—enabled fabless innovation by decoupling design from manufacturing, creating a $130B+ foundry market.