This research explored the influence of patent profile upon firm performance via the advantage of firm size from the three patent indicators - number of annual new granted patents (NANGP), relative patent position of a firm in its most important technological field (RPPMIT), and the Herfindahl-Hirschman Index of patents (HHI of patents) - in the American IC design industry. The results indicated that NANGP and RPPMIT were positively related to firm size, but HHI of patents was negatively associated with firm size. In addition, this study found that there was the advantage of firm size in the IC design industry of US. Therefore, if IC design companies of US want to enhance their firm sizes to capture the advantage of firm size in order to enhance their performances, they should raise their technological competences and their leading positions in their most important technological fields, and cultivate wider technological diversities.