The evolution of inventor networks in the Silicon Valley and Boston regions.

While networks are widely thought to enhance regional innovative capability, there exist few longitudinal studies of their formation and evolution over time. Based on an analysis of all patenting inventors in the U.S. from 1975 to 2002, we observe dramatic aggregation of the regional inventor network in Silicon Valley around 1989. Based on network statistics, we argue that the sudden rise of giant networks in Silicon Valley can be understood as a phase transition during which small isolated networks form one giant component. By contrast, such a transition in Boston occurred much later and much less dramatically. We do not find convincing evidence that this marked difference between the two regions is due to regional differences in the propensity to collaborate or the involvement of universities in patenting. Interviews with key network players suggest that contingent labor mobility between established firms in Silicon Valley, in particular resulting from IBM’s policy as a central player in patenting activity, promoted interorganizational networking, leading to larger inventor networks.