The effect of heat treatments on the microstrueture, composition and electrical properties of the Al/TiW/ Polycrystal1ine Si system was studied systematically for the first time. It was found that Al and Si diffuse through the grain boundaries of the TiW layer at 400°C. Subsequently, Si accumulates at the Al/TiW interface while Al diffuses into the po1ycrystal1ine Si. TiSi, TiSi2, Al3Ti, and WAl10 are formed only at the Al/TiW interface as a result of the heat-treatments for 30min at temperatures between 450 and 500°C. The sheet resistance, measured on the surface of the Al film, is constant up to 350°C and then increases with the heat treatment temperature at all times. The I–V curves are characteristic to Schottky diodes. The general dependece of the current on the applied voltage remains the same but the electrical resistance changes as a result of the heat-treatments. At the long annealing time(30min), the electrical resistance decreases with the heat-treatment temperature. However, at the short annealing times(10–60sec), it first incrsases(between 400 and 450°C) and then decreases (between 450 and 500°C). The results of the electrical measurements are correlated to the microstructural and compositional changes occured due to the heat treatments.