We study the evolution of R&D networks in a Cournot model where

firms may lower marginal costs due to bilateral R&D collaborations.

Stochastically stable R&D networks exhibit the dominant group architecture,

and, contrary to the existing literature, generically unique

predictions about the size of the dominant group can be obtained. This

size decreases monotonically with respect to the cost of link formation

and there exists a lower bound on the size of the dominant group for

non-empty networks. Stochastically stable networks are always inef-

ficient and an increase in linking costs has a non-monotone effect on

average industry profits.