The effect of formalization in high‐growth firms' performance is still unclear. We propose that formal commitment‐based human resource practices contribute positively to the financial performance of established high‐growth firms but have little effect on emergent ones. Using a sample of 101 Portuguese high‐growth firms (2006–2009 period), we tested the effect of formal HR practices during the high‐growth period in their financial results two years later (2011). Our results suggest that adopting a formal performance appraisal and a formal R&D function contributed positively for the performance of only established firms, while adopting a formal training activity negatively affected the performance of only emergent firms.