The semiconductor Cherenkov laser (SCL) is introduced. It is a low-voltage, tunable, far-infrared source of coherent radiation. The SCL exploits the interaction of a relativistic electron beam in close proximity to a semiconductor film. A related device is the Cherenkov free electron laser whose associated theory may be applied to the new device. General expressions for tuning and gain are considered in conjunction with electron beam, optical and material constraints to establish the operating characteristics.