Effectively, a solid-state relay made using transistors; either bipolar junction transistors or MOSFETs can be used. In the ‘switch open’ condition the transistor is in the cut-off condition, or below threshold for MOSFETS; in the ‘switch closed’ condition the transistor is switched fully on – in saturation – and can pass large current with only a small voltage drop. Typical resistance in the on condition is less than 100 ohms.