The most appropriate conditions in the site-controlled anode etching of Al using a mask film for the formation of tunnel pits with high aspect ratios over 20 were examined. Anode etching under a reducing current density at an appropriate ratio against time (200 mA cm(-2) s(-1)) was effective for the suppression of the undesirable lateral dissolution of the Al surface. Moreover, the addition of a small amount of H2SO4 to HCl electrolyte increased the depth of the obtained tunnel pits. By adopting the appropriate anode etching conditions, these improvements could generate site-controlled deep tunnel pits with depths of over 50 mu m.