Introduction : Silicon Control Rectifier is electronic semi-conductor device. Its also known as current controlled device. The name "silicon controlled rectifier" is general electric"s trade name for type of thyristor. The SCR was invented by Gordon Hall and Frank W. "Bill" Gutzwiller in 1957. SCR is unidirectional device so that it conduct current only in one direction. Construction : Silicon Control Rectifier (SCR) is three terminal device(Anode, Cathode, Gate),which consists four layers of semi-conductor, which form NPNP or PNPN structure having three P-N junction terminal i.e J1, J2, J3. Anode (A) terminal is connected to p-layer, and Cathode(K) terminal is connected to n-layer and Gate(G) terminal is connected to p-layer nearest to cathode. Fig-Symbol Of SCR Fig-Silicon Control Rectifier Fig- Actual SCR Operation & Working : There are three mo