We demonstrate a new gain switching mechanism in semiconductor lasers with an asymmetric double quantum well. The idea is to utilize overlap integral enhancement for coupled sublevels in the double quantum well at an applied forward voltage. Optical pulses of less than 10 ps full width at half maximum have been readily obtained with a moderate electrical excitation pulse height, 16.3 V (at a 50 Ω load) and bias current of 6% of the threshold. The advantages of the structure over a single quantum well for generating optical short pulses are shown experimentally.