The innovation activities of new firms are shaped by the knowledge of their founders. Scholars have not reached a strong consensus about whether diverse or specialized founders’ knowledge is more favorable for new firms’ innovation performance. This paper strives to understand how founders’ technological knowledge is associated with innovation productivity as a firm grows. Findings suggest that at the founding stage, new firms with founders who have specialized knowledge are more likely to be productive than new firms with founders who have diverse knowledge. In contrast, new firms with founders who have diverse knowledge tend to be more productive than the others at the growth stage.