To realize a method for interpolating a surface shape of a semiconductor wafer which can accurately interpolate the surface shape with the small number of measuring points.

The method for interpolating the surface shape of the semiconductor wafer comprises the step of obtaining a height of an arbitrary position of the wafer 10 which is disposed at a predetermined interval in a two-dimensional direction and in which a plurality of lattice points are specified in a state in which surfaces are in the same state. The method further comprises the steps of obtaining heights of four measuring lattice points P1, P2, P4 and P5 of adjacent four lattice points to a calculating point P(u, w) to be calculated in height and tangential line data which indicate a height change at the points, calculating tangential line vectors Tu1, Tw1; Tu2, Tw2; Tu4, Tw4; Tu5, Tw5 from coordinates, heights and tangential data of the four measuring lattice points, and calculating the heights of the calculated points from the positional vector and a tangential line vector indicated by the coordinates and heights of the four measuring lattice points by using a polynominal mixture function of a parametric variable.