High-growth firms appear to be key drivers of new industries and technologies. Here we investigate the contribution of these and other types of firm to a technology cluster, in the context of ‘creative destruction’ shaping the evolution of the cluster. Evidence on the reallocation of scarce resources through processes of creative destruction is scarce. But in a cluster the effects of creative destruction can be traced through such developments as (1) firm exits and entries (2) change in firm size distribution and (3) acquisition of firms. We apply churn analysis, firm size transition analysis and analysis of acquisition to the technology cluster in Cambridge UK over twenty years. Firm growth contributed two-thirds of all new job creation, while entry-exit turbulence accounted for one third of job creation. High-growth firms accounted for a quarter of jobs created in the Cambridge cluster during this period, without ever making up more than 3% of all tech firms. There has been an increase in average firm size and profitability. A fall in entry rates and fewer firms moving up into larger size categories in recent years point to adverse conditions for innovative new firms even before the financial crash.