Ferromagnetic-insulator-ferromagnetic trilayer junctions show magnetoresistance (JMR) effects ranging from about 16% to several hundred percent at room temperature. Larger effects are observed when the actual tunneling resistance (R. sub. T) is comparable to electrode film resistance (R. sub. L) over the junction area in cross-geometry junction measurements. The geometrically enhanced large JMR can be qualitatively explained by the nonuniform current flow over the function area when R. sub. T is comparable to R. sub. L, in the cross-geometry junction structure. For a fixed junction area, the effective junction resistance (R. sub. J) can be varied from less than 1 ohm to several kilohms by controlling the thickness of the insulating layer or by appropriately selecting ferromagnetic films. The trilayer tunnel junctions of the present invention are nonvolatile, stable and are reproducible.