High speed optical switches are critical components in the realization of light transmission path switching technology for optical networks. Current Mach-Zehnder Interferometer type optical switches either occupy larger footprint or have a longer one-dimensional scale. A Silicon-based rectangular Mach-Zehnder 2×2 thermo-optical switch unit is proposed for the highly integrated applications. The novel optical switch consists of trench-based nanophotonic frustrated total internal reflection couplers and total internal reflection mirror-based 90° waveguide bends. The switching operation is achieved through thermo-optical effect of Silicon. As a design example, the ~84 μm long L-shape phase-shifting arm is determined for π phase shift when its temperature of the arm is increased up to 50℃. A switching voltage of 3.5 V on a NiCr metal electrode heater is obtained by using finite element method. The voltage may lead to the increase of 50℃ for an optical ridge waveguide in the L-shape phase-shifting arm. The time response of the device is simulated as a function of different upper dielectric thickness of SiO2, and the response time including raise time of 35 μs and fall time of 48 μs is optimized for the device with 0.5 μm thickness of upper SiO2. The switching function of the thermo-optical switch is simulated and verified by Rsoft FullWAVE software, a finite difference time domain method. The chip size of 56×38 μm2 is designed for the Silicon-based rectangular Mach-Zehnder 2×2 optical switch. The device is ultra-compact, and its configuration is beneficial to extend at two-dimensional directions, making them attractive for Silicon-based high dense photonic integrated circuits and on-chip optical interconnect system.