A mechanical relay has a contact mechanism and thus the fundamental problem of contact wear due tong and closing of the contacts, and for this reason theng/closing life of a mechanical relay is limited. A semiconductor relay (or semiconductor switch) solves this problem. Because of this feature, semiconductor relays are being used along with conventional mechanical relays in a variety of markets and applications. Although semiconductor relays have the advantages of a long life and low drive input, these relays have also had such problems as a high offset voltage and high current leakage. Another device similar to a semiconductor relay is a photocoupler. Photocouplers are mainly used for signal switching and signal transmission, and have an optically insulated input.
Semiconductor relays and semiconductor switches made by Matsushita Electric Works include the PhotoMOS relay, which uses a MOSFET for the output element and has optical insulation between the input and output, and the SSR (Solid State Relay), which uses a triac or transistor for the output element.
Responding to the demand in recent years for small portable devices, small semiconductor switches are being used in wireless communication devices such as cell phones for applications such as signal path switching, radio wave transmission-reception switching, and frequency switching.
Matsushita Electric Works' hybrid MEMS relays have the following advantages compared to semiconductor switches:

• Excellent isolation characteristics.
• Large power handling.
• Small insertion loss.
• Excellent environmental characteristics concerning heat, such as ambient temperature.
• Chemical substances that adversely affect the environment such as those stipulated in RoHS are not used; the relays are environment-friendly.