We examine the effects of avalanche processes on several classes of nonlinear optical interactions in semiconductor junctions. A silicon avalanche photodiode (APD) geometry is predicted to provide large enhancements of both the electronic nonlinearity (free‐carrier plasma interaction) as well as the thermal nonlinearity. The thermal nonlinearity at a wavelength &lgr;=1.06 &mgr;m in an APD is examined under normal operating conditions and a nonlinear interaction more than 5000 times that of the unbiased diode is observed.