We successfully improved a merged diamond diode, namely a Schottky‐pn diode (SPND), which is composed of a fully depleted n‐type active layer sandwiched between a highly doped p+‐type layer and a Schottky metal. According to the analysis of operation mechanisms based on band diagrams, we increased the acceptor concentration in the p+‐type layer in order to decrease the on‐resistance (RonS), and increased the n‐type layer width to reach higher blocking voltage (Vblock). Consequently, much lower RonS of 0.03 mΩ cm2 and higher Vblock than those of the previously reported diamond SPND were achieved simultaneously. Thus, we elucidated experimentally that the diamond SPND has no trade‐off relationship between RonS and Vblock, and is suitable for low‐loss high‐power switching devices.