Abstract We apply the Ising Model in a Transverse Field (IMTF) to analyse the properties of a potassium dihydrogen phosphate/potassium dideuterium phosphate (KDP/KD ∗P) superlattice. This is particularly simple because the main difference in the experimental parameters of the constituents is between the transverse fields; the exchange constants differ only by about 10%. Numerical mean-field theory is applied to calculate the on-site polarization and dielectric susceptibility and their spatial averages 〈〈 P〉〉 and 〈〈 χ〉〉, which are the macroscopic values for the superlattice. We also calculate the macroscopic pyroelectric coefficient p. Thick-layer superlattices, e.g. 25/25, show two peaks in 〈〈 χ〉〉 and p, as if they had two phase transitions, whereas thin-layer superlattices, e.g. 5/5, show one-peak behaviour.