The switching ratio, the ratio between the thermal conductance in its off and on states, of a thermal switch is a critical design parameter of such a device. Here, we propose Peltier modules as a type of all-solid-state thermal switch that can operate over a wide temperature range and with an adjustable switching ratio. Calculations show that the switching ratio depends only on thermoelectric figure of merit and temperature bounds. A Peltier couple is constructed from Bi2Te3-based material and characterized by its thermal conductance and response time in the open condition and under an optimal activation current. The switching ratio diverges at small temperature differences with record-high measured values, an order of magnitude larger than achieved by other solid-state devices near room temperature. Materials with a high figure of merit could produce even larger switching ratios over higher temperature differences. (C) 2019 Elsevier Ltd. All rights reserved.