Inventor Mobility, Knowledge Spillovers and Spinoff Entry in the U.S. Semiconductor Industry: Regional Patterns, Determinants, and Learning Implications

This dissertation systematically analyzes the link between inventor mobility and knowledge diffusion in the semiconductor industry. It looks at how incumbents and recent entrants benefit from hiring inventors by analyzing geographical mobility patterns, the determinants of inventor mobility, and the types of learning that results from hiring. The analysis is based on data on the origins of all semiconductor producers with larger sales, and on patent filings and patent citations. Three papers comprise the dissertation. The first paper argues that the higher mobility of inventors in Silicon Valley can be explained mostly through the rate of spinoff entry in the region. The empirical evidence shows that inventor mobility was high in Silicon Valley since spinoffs started entering in large numbers, which happened before the industry clustered there. Agglomeration economies and the ban of non-compete covenants can facilitate the continued entry of spinoffs, but they cannot explain the initial wave of entry. Further evidence of the effect of entry on mobility rates is provided by spinoffs outside of Silicon Valley, which also hire many inventors from their parents and other local firms. The second paper identifies and tests several drivers of worker turnover associated with matching and learning. Incumbents, recent entrants, and spinoffs have different goals when hiring experienced inventors. Incumbents hire many workers without prior patents, while younger firms hire mostly experienced inventors. For inventors hired by incumbents, the main determinant is matching. Instead, movements from parent to spinoffs seem to be motivated by the acquisition of knowledge from the parent. None of the drivers previously identified seem to apply to recent entrants. The last paper analyzes the effect of hiring experienced inventors on the citations made by the hiring firm. In movements to incumbents, or from parent to spinoffs, there is an increase in citations from the hiring to the origin firm. However, movements to recent entrants are associated with increases in citations to other firms. This is related to what firms learn from hiring. While incumbents and spinoff access firm specific knowledge from moving inventors, recent entrants seem to be more concerned with the knowledge about the industry that the inventor possesses.