The conduction‐band discontinuities and interface charge densities of severaln‐Nisotype InxGa1−xAs/InP (x&bartil;0.53) heterojunctions with lattice mismatches (&Dgr;a/a) ranging from +0.26 to −0.24% were measured using capacitance‐voltage techniques. To facilitate these measurements, organic‐on‐inorganic contact barrier diodes were used. Extremely low interface charge densities (<1×1010cm−2) are obtained for all the samples, which are approximately one order of magnitude lower than previously reported values for these heterojunctions. We find that the interface charge density is independent of the magnitude of lattice mismatch and temperature. All the samples show a clear peak‐and‐notch in their apparent free‐carrier concentration profiles at temperatures as low as 83 K. This is in contrast to results reported previously where the notch is observed to disappear at low temperature. The measured heterojunction conduction‐band discontinuity is also found to be temperature independent, with a value of 0.22±0.02 eV.