In the Institute for Microstructural Sciences we have been developing a surface micromachining process for the fabrication RF MEMS on quartz substrates. In a previous paper we reported on the microwave performance of these switches [1]. In this paper we report on the characterization of the switch mechanical properties as a function of temperature. Real world electronic devices must meet a minimum of 0°C to 70°C operation range. Many devices must work in the range of −40°C to 85°C such as portable devices like hand phones. Since we are developing a relatively unique process, we do not have a reference that indicates how our MEMS device will behave as a function of temperature. Since the device uses silicon nitride for the main suspension and the substrate is quartz, we expect to find temperature dependent stress due to difference in expansion coefficient. We have also found that the metals used for the electrostatic actuator may change properties with low temperature 50°C annealing. Hence we are concerned with the possibility of hysteretic behaviour. We focus on the mechanical stiffness or spring constant. This is a key parameter in determining the actuation voltage. Any changes in this parameter would be an indicator of a long term reliability problem. We are testing our devices in the temperature range 10°C–80°C using the apparatus shown in Figure 1.