A robust design of RF MEMS capacitive shunt switches was implemented with a movable gold membrane, separate and non-contacting actuation pads, and electrostatic actuation. The same design was fabricated on silicon and quartz substrates with different combinations of dielectric constant, resistivity, thermal conductivity, and thermal expansion coefficient. It was found that most switches could operate between 0°C and 60°C and handle hot switching up to at least 5.6 W. However, the pull-in voltage of the switches fabricated on quartz had stronger temperature and power dependence than that on silicon. This was attributed to greater thermal expansion mismatch, impedance mismatch and self-heating on quartz. These results show that the power-handling capacity of a switch is determined by not only its membrane design, but also its circuit environment.