The influence of surface tension becomes more prominent as the device is miniaturized. We used this effect to enhance the detection sensitivity of trace heavy metal ions. A microelectrode array was formed along with a Ag/AgCl reference electrode and was surrounded by a super-hydrophobic layer formed with polytetrafluoroethylene (PTFE) beads. When a droplet of a sample solution was placed on the sensing area, the super-hydrophobic layer repelled the solution and a spherical droplet was formed. The droplet shrank to the sensing area as the solution evaporated. Electrochemical preconcentration was then carried out with the concentrated solution. Three heavy metal ions (Cd2+, Pb2+, and As3+) were analyzed by square-wave anodic stripping voltammetry. A significant increase in current peaks was observed by this novel method. When a 10-µL droplet was used, the detection limit was 600 ppt for Pb2+ and As3+ ions and 900 ppt for Cd2+ ions. Furthermore, the effect of the evaporative concentration was enhanced by increasing the volume of sample solution. We used this device for analysis of real samples. Correlation between the values obtained by this method and a conventional method was satisfactory with correlation coefficients of 0.982 (Pb2+), 0.969 (Cd2+), and 0.936 (As3+). Copyright © 2009 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.