Thermionic emission rates are reported for electrons in GaAs epilayers, where electrostatic barriers within the layers and GaAs/AlAs heterojunctions form different sides of the potential well. Attempt times at the two barrier types were observed to differ by factors above 107due to differing constraints on momentum conservation during emission. These emissions represent escape mechanisms for charge stored in a closed geometry, III‐V compound floating gate transistor, with potential application as dynamic random access or nonvolatile memories.