The steady‐state charge‐balance‐related properties of semiconductor junctions between highly dopedn‐type epitaxial layers of GaAs and semi‐insulating GaAs substrates are examined. Specific results are obtained for the three most common defect compensation mechanisms within the semi‐insulating material: (i) a deep donor interacting with a shallow acceptor, typified by the case of the EL2 defect and background carbon, respectively; (ii) a shallow donor and a deep acceptor, as would occur for heavy levels of silicon and chromium; and (iii) a deep donor and a deep acceptor, as would be typical of EL2 and light levels of either chromium or a complementary antisite defect. Electrostatic properties, including Fermi‐level positions, built‐in potentials, asymptotic electric‐field profiles, and junction capacitance are analytically derived based upon Hall/Shockley–Read models of the defect states and these are additionally compared against numerical solutions which implement the same models. Junction boundary conditions that pertain to the high‐level injection case normally encountered in these junctions are also analytically derived and verified by numerical simulation. Limitations on the applicability of standard step‐profilep‐n–junction theory are discussed, as are necessary considerations for proper numerical modeling.