To provide a precision polishing method for a semiconductor substrate and device thereof allowing improvement of positioning accuracy by polishing film layers on an alignment mark for positioning into symmetrical shapes, prevention of the transfer of a grid-shaped groove pattern cut on the surface of a polishing pad and improvement of micro flatness.

Total polishing time T, rotational speed switching time t, rotational speed N1 for wafer W before the rotational speed switching time t, rotational speed N2 for the wafer W after switching of rotational speed and rotational speed (N1-n) of the polishing pad P before the rotational speed switching time t are set. Rotational speed Nx of the polishing pad P after switching of rotational speed is calculated so that total rotational numbers in the wafer W and the polishing pad P may be coincident, the wafer W and the polishing pad P are rotated and driven and the wafer W is polished. As a result, the film layers on the alignment mark on the wafer W can be isotropically polished and positioning accuracy can be improved.