We fabricated highly doped Si single-electron transistors (SETs) with a series of geometrically defined multiple islands. Highly doped SETs have the advantage of being easy to fabricate. Moreover, SETs with multiple islands provide a larger peak-to-valley current ratio (PVCR) than SETs with a single island. A PVCR for the Coulomb oscillation of up to 77 was observed at room temperature. This large PVCR is advantageous for circuit operations. We applied the Coulomb oscillation and multiple-gate input characteristics of only one SET to obtain an exclusive-OR operation at room temperature.