The sheet resistance for a microarea in a large silicon wafers was measured by using a modified Rymaszewski's formulas for a square four-point probe technique. An improved Rymaszewski's formulas was deduced taking into account the shift of probes in square four-point probe measurement. The equation of resistivity for square four-point probe measurement when there were shifts of the probes and there was no shift of the probes was deduced theoretically. A possible error produced by the shift of the probes was analyzed in theory and expressed with graphs. The effect upon measuring results arising from the shift of probes was also discussed. Practical-measurement of a specimen has been tested using a self-established equipment of square four-point probes. An equal-value-line graph was plotted for the measurement-results.