Thermal switch for rapid thermal coupling and decoupling of devices under test

An apparatus for testing integrated circuits (ICs) , includes a first thermal contact structure having a first surface to interface with a heat source and an opposing second surface to interface with a device under test (DUT). A second thermal contact structure is above the first thermal contact structure and separated therefrom by a variable-resistance thermal interface (VRTI) structure operable to couple or decouple the first and second thermal contact structures from one another. The VRTI structure has a maximal thermal conductivity associated with a first state, and a minimal thermal conductivity associated with a second state.