The focus of this theoretical study is price competition when some firms operate their own branded website while others sell their products through an online platform, such as Amazon Marketplace. On one hand, selling through Amazon expands a firm’s reach to more customers, but on the other hand, starting a website can help the firm to increase the perceived value of its product, that is, to build brand equity. In the short run the composition of firms is fixed, whereas in the long run each firm chooses between Amazon and its own website. I derive the equilibrium prices and profits, analyze the firms’ behavior in the long run, and compare the equilibrium outcome with the social optimum. Comparative statics analysis reveals some interesting results. For example, I find that the number of firms that choose Amazon may go down in response to an increase in the total number of firms. A pure-strategy Nash equilibrium may not exist; I show that price dispersion among firms of the same type is more likely in less concentrated markets and/or when the increase in the perceived value of the product is relatively small.