A scheme for Q -switching semiconductor lasers is proposed and analyzed. The method is based upon electrooptic switching of the Bragg reflectivity of the grating reflectors forming the cavity of the semiconductor laser. The basic configuration, the operating principles, and the dynamic behavior of these lasers are described. Although the maximum initial inversion in this laser system is limited to a rather low value, the peak output power is found to be higher than the value usually obtained in a CW GaAs double-heterostructure (DH) laser by two orders of magnitude. A pulsewidth shorter than 100 ps is shown to be obtainable.