We present calculations of tunneling transmission coefficients for electrons through (100) GaAs-Ga1−xAlxAs–GaAs heterostructures. The calculations were performed using the empirical tight binding approximation. For sufficiently thick alloy regions, the tunneling probability is an exponential which decays with alloy thickness multiplied by a prefactor which is independent of alloy thickness. We have investigated the dependence of the tunneling prefactors on incident electron wavevector and alloy composition x. For the prefactors, we find a strong dependence on the incident electron wavevector component, normal to the interfaces and the alloy composition x, and a weak dependence on the incident electron wavevector component parallel to the interface for the energy range of interest.