Hybrid transistor based power gating switch circuit and method

A method includes forming a first transistor having a first gate dielectric thickness and a first source/drain extension depth, a second transistor having a second gate dielectric thickness and the first source/drain extension depth, and a third transistor having the second gate dielectric thickness and a second source/drain extension depth. The second source/drain extension depth is greater than the first source/drain extension depth. The second gate dielectric thickness is greater than the first gate dielectric thickness. The first transistor is used in a logic circuit. The third transistor is used in an I/O circuit. The second transistor is made without extra processing steps and is better than either the first or third transistor for coupling a power supply terminal to the logic circuit in a power-up mode and decoupling the power supply terminal from the logic circuit in a power-down mode.