There is growing institutional and social pressure for greater balance, parity, and equality at the highest levels of corporations. This is coupled with an increasing interest in analysing the effects of gender diversity on corporate boards. However, companies may only reap the benefits of gender diversity by achieving better qualified and more independent boards. This study aims to contribute to the open debate on the effects of board gender diversity on R&D, by taking into account the independence of female directors. Panel regression analyses were performed with data for 67 Spanish-listed companies during the 2003–2019 period. Our results confirm the positive effects of gender diversity on R&D. However, this positive influence is lower if female directors have family links with male members on the board. These findings have policy implications, regarding the need to increase gender equality in corporate boards for social and sustainability purposes, while the benefits are conditioned by the independence of female directors. The value of this research rests on the study of the effects, beyond the mere analysis of financial performance of the gender diversity of boards.