Disclosed is a Gunn-effect device comprising, for example, a crystal of n-type gallium arsenide having alloyed contacts (e.g., indium and gold) which is switched from one frequency of oscillation to another by controlling the incident light while maintaining an appropriate temperature and bias voltage. It is believed that trap zones which are localized within the crystal by virtue of introducing acceptor impurities account for a frequency of oscillation different from the usual transit-time frequency. The Gunn domains and the incident light are made to dynamically perturb the trap system so as to achieve a nonequilibrium condition.