The sheet resistance of square microareas with an area of 100 × 100μm2 can be determined by using a modified Van der Pauw's method. In this method, the tip positions of the four probes are controlled respectivly at the four corners out side the inner tangential circle of square microareas by direct inspection using a microscope with a magnification of 8 × 10. The measurement results are independent of wanderings of probes and it is not necessary to determine the precise positions of probes in order to make corrections for the boundary effect. These conclusions are proved in this paper by using FEM and have been confirmed by the determination of sheet resistance of gold microbumps.