We experimentally demonstrate surface-emitting second harmonic generation in a waveguide containing asymmetric coupled GaAs/AlGaAs quantum wells. The nonlinear conversion efficiency is enhanced by reversing the asymmetric well orientation every coherence length, in order to quasiphase match the vertical second harmonic generation process. The measured spectrum of the asymmetric quantum well susceptibility is dominated by an excitonic peak at a pump frequency corresponding to half of the first electron-heavy hole transition energy. ©1997 American Institute of Physics.