Gas turbine engine has been widely applied to many heavy industries, such as marine propulsion and aerospace fields. Increasing turbine inlet temperature is one of the major ways to improve the thermal efficiency of gas turbines. Internal cooling for gas turbine cooling system is one of the most commonly used approaches to reduce the temperature of blades by casting various kinds of ribs in serpentine passages to enhance the heat transfer between the coolant and hot surface of gas turbine blades. This paper presents an investigation of the boot-shaped rib design to increase the heat transfer performances in the internal cooling turbine blades for gas turbine engines. By varying the design parameter configuration, the airflow is taken with higher momentum, and the minor vortex being at the front rib is relatively removed. The object of this investigation is increasing the reattachment airflow to the heated wall and reducing the vortex occurring near the rib for improving the performances of heat transfer using three-dimensional (3D) Reynolds-averaged Navier–Stokes (RANS) with the SST model. A parametric study of the boot-shaped rib design was performed using various geometric parameters related to the heel-angle, toe-angle, slope-height, and rib-width to find their effect on the Nusselt number, temperature on the ribbed wall, friction factor ratio of the channel, and thermal performance factor. The numerical results showed that the heat transfer performances are significantly increased with the heel-angle, toe-angle, slope-height, while that remained relatively constant with the rib width.