Hydrodynamic gas film bearings are widely used for very-high-speed, lightly loaded rotating machinery. In the design of hydrodynamic gas film bearings, it is of cardinal importance to enhance the stiffness of gas films to minimize vibration due to external excitations. Among various types of hydrodynamic gas film thrust bearings, grooved bearings have an advantage of high stiffness and load-carrying capacity, but the stiffness of the bearings strongly depends on groove geometry. Therefore, when the groove geometry is suitably designed, it is expected to considerably improve the stability characteristics of the bearings. However, conventional bearing geometries are based on a fixed logarithmic spiral curve, and there is no literature on how to effectively change the groove geometry to drastically improve the bearing characteristics. In this paper, the entirely new optimum design methodology, in which the groove geometry can be flexibly changed by using the spline function, is presented to maximize the stiffness of gas films for grooved thrust bearings. The effectiveness of the methodology is experimentally verified.