We incorporate Co thin layers into the quadrilayer structure of glass/Cu/SnO2/Co/SnO2 and investigate the effect of transparent semiconductor SnO2 as cap and spacer layers on the magnitude of a magneto-optical Kerr signal. The theoretical calculations based on a 4 × 4 matrix method are exploited to find the best possible multilayer structure. Accordingly, we fabricate several samples and acquire large Kerr signals in both polar and longitudinal geometries. Furthermore, the effect of vacuum annealing on the magnetic response of the samples is investigated. It is revealed that annealing at high temperatures may reduce the Kerr response because of uncontrolled heat-induced interdiffusion of adjacent layers.