Leakage currents in epitaxial ferroelectric/perovskite‐conductor heterostructures reproducibly show diode properties having hysteresis. The hysteresis appears in forward bias, which is positive for electron (n) type conductors and negative for hole (p) type conductors. The hysteresis is due to the increase of conductivity by the forward bias current, which exhibits the memory retention for more than an hour. The write and erase speeds of the diode and the origin of the effect are discussed. ©1995 American Institute of Physics.