A picosecond optical gate controlled by optical pulses has been demonstrated with a traveling-wave (TW) semiconductor laser amplifier (SLA). The gate uses two kinds of optical pulse, one for carrier generation and the other for carrier recombination. The operating principle of the gate is explained. The gate response time depends on the width of the pulse injected into the amplifier and is limited to the intraband relaxation time, which is of the order of subpicoseconds. Streak camera measurements are shown and discussed. The measured rise and fall times are limited by pump and control pulse width and can be shortened by using shorter pulses. Rise and fall times of 28 and 49 ps respectively, have been obtained for 1.2-pJ optical pulses. The extinction ratios were 4 dB and 8 dB, respectively.