本文以一個簡單賽局理論模型為分析依據,探討企業間的自製或是外包策略對整體社會福利的影響。 傳統經濟理論分析告訴我們自製策略可以解決雙重邊際化的問題。但在本文我們舉出一個反例，亦即當存在研發的可能及上下遊市場的研發外溢效果時，垂直整合可能會造成廠商過度研發的情形，最終產生整體社會福利不效益情形。 / In this paper, we set up a game-theoretic model, in which the whole industry is composed of a downstream monopolist and two upstream firms. This paper discusses the major debate in a firm’s market strategy: to make or to buy the components it needs. Traditionally, economic theories told us that vertical integration strategy (make strategy) can solve the problem of double marginalization and hence increase profits as well as social welfare. Nevertheless, this result does not necessarily hold when R&D possibility is introduced. We show that when there is downstream to upstream R&D spillover, vertical integration may result in an over-investment in R&D from the social standpoint. This result may shed some light on the rationale behind recent antitrust rulings.