本論文旨在分析新貿易保護主義下，美國關稅政策如何影響外國廠商在出口與對外直接投資之間的策略選擇。本論文建構一個具有上下游關係的垂直相關市場模型，將台灣廠商設定為上游中間財供應者，韓國廠商設定為下游最終財供應者，並假設兩國廠商於美國市場中面臨 Cournot 數量競爭。透過逆向歸納法，本論文先分析兩國廠商皆採出口時，關稅變動對產量、價格與利潤之影響，再進一步將對外直接投資納入廠商策略選擇，探討固定設廠成本與關稅水準如何影響均衡結果。 研究結果顯示，關稅政策的效果並不僅限於被課稅廠商本身，而會透過垂直市場結構產生間接影響。當美國提高對台灣中間財之關稅時，台灣廠商出口成本上升，可能提高其赴美投資誘因；但同時也會推高中間財價格，影響美國下游廠商成本，並改變韓國廠商在最終財市場中的產量及利潤。相對地，當美國提高對韓國最終財之關稅時，韓國廠商出口成本上升，可能促使其轉向對外直接投資；但此一政策亦會透過美國下游廠商產量變化，進一步影響台灣廠商的中間財需求與投資誘因。 此外，本論文發現，當固定設廠成本較低時，廠商較可能選擇對外直接投資以規避關稅；當固定設廠成本較高時，廠商則可能維持出口。若關稅或固定成本位於中間區間，則可能出現一方出口、另一方對外直接投資，甚至多重均衡的結果。整體而言，本論文說明，在垂直相關市場中，關稅政策不僅會影響外國廠商自身的出口與投資決策，也會透過上下游市場連動，改變其他廠商的策略誘因。;This thesis examines how U.S. tariff policies under the new wave of trade protectionism affect foreign firms’ strategic choices between exporting and FDI (foreign direct investment). A vertically related market model is developed in which Taiwanese firms are assumed to be upstream suppliers of intermediate goods， while Korean firms are assumed to be downstream producers of final goods. Firms compete in the U.S. market under a Cournot quantity competition framework. Using backward induction， the thesis first analyzes the effects of tariff changes on output， prices， and profits when both foreign firms serve the U.S. market through exports. It then incorporates FDI as an alternative entry mode and investigates how fixed investment costs and tariff rates influence equilibrium outcomes. The results indicate that the effects of tariff policies are not limited to the firms directly subject to tariffs， but also generate indirect effects through the vertical market structure. When the United States increases tariffs on Taiwanese intermediate goods， Taiwanese firms face higher export costs， which may strengthen their incentives to undertake FDI in the United States. At the same time， higher tariffs increase intermediate-goods prices， raise production costs for U.S. downstream firms， and alter the output and profitability of Korean firms in the final-goods market. Conversely， when the United States raises tariffs on Korean final goods， Korean firms face higher export costs and may switch from exporting to FDI. Such policies also affect Taiwanese firms indirectly through changes in the output decisions of U.S. downstream firms， thereby influencing the demand for intermediate goods and the incentives for Taiwanese firms to invest abroad. Furthermore， the analysis shows that firms are more likely to choose FDI when fixed investment costs are relatively low， whereas exporting remains the preferred strategy when fixed investment costs are high. When tariff rates or fixed investment costs fall within intermediate ranges， asymmetric equilibria may emerge， in which one firm exports while the other undertakes FDI. Multiple equilibria may also arise under certain conditions. Overall， the findings suggest that， in vertically related markets， tariff policies not only affect foreign firms’ own export and investment decisions but also reshape the strategic incentives of other firms through upstream–downstream market interactions.
