Aluminum/chemical vapor deposited tungsten (Al/CVD-W) interconnects shows an undesirable large increase in sheet resistance due to Al-W reaction during annealing at 450 degrees C. The effect of native oxides on W surfaces on the resistance increase has been studied. When there is no native oxides on W surfaces, the narrower interconnects show a larger increase in sheet resistance after annealing due to the nonuniform formation of WAl12. On the other hand, the interconnects with the native oxide at the Al/W interface show a large increase in sheet resistance, which has little dependence on linewidth. This is because WAl12 formation is suppressed by Al-2(WO3)(4) and WAl5 formation.