A tri-modal multi-threshold CMOS (MTCMOS) switch design is presented. Similar to the conventional MTCMOS switches, the tri-modal switch comes in two flavors: header and footer. The tri-modal switch provides three different power modes for the underlying circuit: active, drowsy, and sleep. The ability of data retention in the drowsy mode makes the proposed tri-modal switch an excellent candidate for implementing data-retentive power gating designs. We will see that three different low-power design schemes, namely data-retentive power gating, multi-drowsy mode structures, and on-chip dynamic voltage scaling, are implemented using the proposed tri-modal switch. We show that our proposal introduces superior low-power solutions across various circuit operating modes using a single circuitry.