With two coherent waves incident to a two‐dimensional (2D) nonlinear optical superlattice containing Kerr form dielectric nonlinearity, the optical bistability related to transition between a forbidden transmission state and an allowed transmission state can occur through the index‐modulation mechanism. This kind of bistability is difficult to obtain in the case of only one incident wave. The power cost for the bistability might be very low. ©1995 American Institute of Physics.