本文以垂直相關市場的架構來分析外人直接投資模式的選擇及福利效果。研究結果顯示，相較於綠地投資的情況，均衡中間財價格在跨國併購下較高。基於此中間財價格效果，均衡的投資模式與國內外廠商之間的成本差異程度兩者具非單調之關係。當此成本差異程度較大或較小時，外國廠商的最適投資模式爲綠地投資；若該成本差異程度適中，則跨國併購爲最適的投資模式。本文也探討不同投資模式對地主國社會福利的影響。我們發現外國廠商所選擇的投資模式與地主國福利極大所偏好者並不一致。

This paper analyzes the mode choice of foreign direct investment and the resultant welfare effects assuming vertically related markets. Results show that the intermediate good price is higher for cross-border merger and acquisition than for greenfield investment. Due to this intermediate-good price effect, in equilibrium, there is a nonmonotonic relationship between the investment mode and the cost difference between the foreign firm and the domestic firms. If the cost difference is either sufficiently large or sufficiently small, the foreign firm chooses greenfield investment; if the cost difference is in middle ranges, cross-border merger and acquisition is the optimal investment mode. We also investigate the welfare effects of different investment modes for the host country, showing that the foreign optimal and the socially desirable investment modes are inconsistent.