Tunneling experiments were done on YBa2Cu3O7 step‐edge junctions. The temperature dependence of the superconducting gap parameter, Δ(T), was measured. From the peak‐to‐peak distance in the conductance curve, Δ was estimated to vary from 24 to 32 meV at 4.2 K. The conductance at high‐voltage bias does not increase with increasing voltage. The tunneling results, together with the well‐behaved magnetic field dependence of the critical Josephson current, hysteresis, and Fiske‐type resonances in current‐voltage curves, indicate a dielectric behavior of the grain boundary junction, i.e., a tunnel junction. © 1996 American Institute of Physics.