We have carried out laser‐induced grating and nonlinear transmission measurements near the band gap of amorphous Si:H. The nonlinear four‐wave mixing response deviated substantially from traditional third‐order effects. An intensity dependence of less than cubic for the diffracted intensity was observed. The nonlinearity does not follow the absorption profile. An effective nonlinear susceptibility &khgr;(3)=5×10−9esu was found at 572 nm. The nonlinear transmission showed saturable absorption at low intensities, and induced absorption at high intensities. This behavior can be attributed to light‐induced defects.