固态继电器（Solid State Relay，缩写：SSR）是由半导体控制负载流经固态开关的无接点继电器，输入端系利用发光二极管、光晶体管、功率晶体等半导体电路所组成光耦合器，经内部控制电路触发输出端的硅控整流器（SCR）或双向硅控整流器（TRIAC）进而导通负载电流，因此可以接受低压直流或交流信号输入之后，进而导通高压、高功率之输出电流，具隔离输出入及控制高功率输出电流之效果。

有些SSR也包含了突波吸收线路或零交越侦测器以减少由负载电流中断所产生火花及暂态。虽然组件中半导体能散热，但是SSR经常还是需要装在散热片设备上以减少产生温度。 SSR通常使用在传统电磁继电器在快速ON/OFF周期时容易损坏的应用，一般用SSR有高达10万次开关周期生命，而且SSR还可以使用传统CMOS及TTL逻辑电路去激磁。

A solid-state relay (SSR) is an electronic switching device that switches on or off when a small external voltage is applied across its control terminals. SSRs consist of a sensor which responds to an appropriate input (control signal), a solid-state electronic switching device which switches power to the load circuitry, and a coupling mechanism to enable the control signal to activate this switch without mechanical parts. The relay may be designed to switch either AC or DC to the load. It serves the same function as an electromechanical relay, but has no moving parts.