Variable reactance epitaxial siliconp‐njunctions with approximately constant impurity gradients were investigated at 5.85 Gc/sec, 1 Mc/sec and dc between room temperature and 2°K. Thep‐njunctions were B‐P and B‐As doped. The units with breakdown voltages larger than 11V (at 300°K) showed an exponential freeze‐out of the carriers at 5.85 Gc/sec when the temperature was lowered. The units with less than 7.7 V breakdown voltage showed clearly impurity band conduction at low temperatures. The maximum change of the reactive component between large forward currents and the breakdown voltage was temperature independent within ±10% for all the wafers. The cutoff frequencies of the wafers at 300°K were between 190 and 320 Gc/sec. The units with large breakdown voltages (>14 V) had a negative differential resistance in the dc forward voltage‐current characteristics at low temperatures. From an extrapolation of the present experiments one would expect, when the impurity gradient at the junction is increased to such a value that the breakdown voltage is about 5.5 V, that epitaxial silicon variable reactancep‐njunctions will operate at microwave frequencies and liquid‐helium temperatures with approximately the same losses as at room temperature.