We reveal the intrinsic Josephson effect in aLa2−xSrxCuO4(LSCO) high-Tcsuperconductor. Nb counterelectrodes are deposited on top of mesas, which are formed on surfaces either parallel or perpendicular to theabplane of LSCO single crystals. Nb/LSCO interfaces behave as SNS Josephson junctions. For the junctions parallel to theabplane, we observe many branches in the current–voltage characteristics due to intrinsic Josephson effects. The voltage gaps between the branches are typically 0.1 mV, which is much smaller than the superconducting energy gap 2&Dgr;≅11 mV expected for LSCO from Bardeen–Cooper–Schrieffer theory. ©1998 American Institute of Physics.