A Note on Endogenous Market Structure under Heterogeneous Firms *

Industries, such as semiconductors and biotechnology, are characterized by heterogeneous research productivity and vertically differentiated products. In this note, I relax the assumption of symmetric R&D costs in Sutton [1998] and derive the lower bounds to market concentration when entry and R&D investments in product quality are jointly determined. I show that the lower bound to concentration depends on the degree of vertical differentiation, which is a function of market size and quality choices. My findings imply that empirical applications that fail to account for differences in quality will be biased towards the null hypothesis of exogenous entry costs otherwise.