A balance between static and dynamic losses of a power MOSFET is always desirable for accomplishing the maximum efficiency for a specific power converter. The standard semiconductor theory suggests that a minimum power dissipation in a MOSFET can be achieved by selecting a specific device active area. However, for power circuit designers, the active device area is unknown given that only datasheet parameters are available. Hence, in this paper, we propose a simple method, based on semiconductor theory, to select optimum power MOSFET from a family of MOSFETs using only datasheet parameters. By applying this optimization method to the specific power supply circuit under development, power engineers can select the best transistors to yield lowest power losses for the systems under development.