We report spin-dependent perpendicular transport in the magnetic trilayer junction structureLa0.67Sr0.33MnO3/SrTiO3/La0.67Sr0.33MnO3.Large (factor of 5) changes of magnetoresistance induced by a field of∼200Oe are observed at4.2K. JunctionI–Vcharacteristics at low temperatures are consistent with a metal–insulator–metal tunneling process with a large spin-polarization factor of0.81for the conduction electrons. Above100K, a variable range-hopping conduction shunts out the magnetoresistance contribution. This second conduction channel comes from the impurity states within SrTiO3barrier and therefore is not an intrinsic limit to the magnetoresistance performance of the device at high temperatures. ©1997 American Institute of Physics.