An extensive literature has examined the role of worker mobility for the diffusion of knowledge. For the most part, this literature has focused on large firms. We draw from the literatures on organizational learning, strategy and entrepreneurship to examine different ways in which new firms benefit from hiring experienced workers. We propose the needs of incumbents, in terms of knowledge acquisition, are different from the needs of spinoffs and de-novo entrants: While incumbents hire experience inventors to acquire specific pieces of knowledge, recent entrants hire experienced inventors to build up the firm capabilities. In the case of spinoffs, they also hire many inventors from their parents to obtain knowledge related to the idea that led to the spinoff. Using patent data and detailed information on the origins of merchant semiconductor producers, we analyze how spinoffs and other recent entrants leverage the previous knowledge of the first inventors they hire. Results show that most patenters at new firms have prior patenting experience, while most patenters at incumbents have no prior patents. Hiring inventors from incumbents, and in particular from leading incumbents, increase the probability of entrants using knowledge from other firms. However, in contrast to what happens at incumbents, this knowledge is not necessarily something developed at the mobile workers’ prior employers. We discuss the implications of our findings for understanding how entrepreneurial activity may be affected by policies that aim to restrict worker mobility, and by the availability of knowledgeable mobile workers in industry clusters.