This paper describes the performance of stainless-steel micro-relays, with platinum-rhodium metal foil contact elements, in handling high-power RF signals. The electrical and thermal responses are described for electrostatically actuated three-terminal micro-relays that are directly assembled on printed circuit boards. The preliminary designs have footprints of 6.4 mm2. Fabricated relays have 90-V turn-on (pull-down) voltage. The down-state insertion loss and up-state isolation were better than 0.2 and 25 dB over the band of dc-5 GHz, respectively. The devices can accommodate incident RF power up to 18.5 W at 3 GHz when cooled by forced air from a mini-fan.