We have prepared Ba1−xKxBiO3grain‐boundary junctions on SrTiO3bicrystal substrates and observed the quasiparticle tunneling current for a superconductor–insulator–superconductor (SIS) junction. The current–voltage (I–V) characteristics were investigated by using a gap‐energy distribution model to consider the effect of the inhomogeneity of &Dgr; at the grain‐boundary junction interface. The broadening of theI–Vcharacteristics around the gap voltage of a SIS junction and its temperature dependence could be explained by assuming the Gaussian distribution of gap energies with &Dgr;0(0)=3.8 meV and &dgr;&Dgr;=0.8 meV, where &Dgr;0(0) and &dgr;&Dgr; denoted the mean value and variance of the distribution, respectively. ©1995 American Institute of Physics.