In this paper a general formula was derived for semiconductor resistivity measurements, in which four probes may be set in any positions. From this formula, we have obtained a general expression for calculating the probe-wander error; and the transverse probe-wander as well as the longitudinal probe-wander error have been considered simultaneously. So, we can evaluate the probe-wander errores of linear probes and square probes. In addition, we have derived the probe-wander error in sheet specimens measurements with these two kinds of probes. Theory has indicated that the probe-wander error cannot be ignored in an accurate measurement. Lastly, we have discussed the methods of eliminating or decreasing the probe-wander error.