Bistability in the spectral output of a two‐section cleaved‐coupled‐cavity (C3) semiconductor laser is observed. A wide (10 mA) and temperature insensitive hysteresis loop is obtained at laser currents up to at least 3×Ithand the laser can be switched with subnanosecond electrical pulses between its two spectraly pure states. The switching is characterized by a power‐delay product of 4×10−12J and a switching time of less than 1 ns.