A method of adjusting the parallelism of a surface of a block of optical fibers with a surface of a semiconductor chip or wafer laid on an XY table, including the steps of: a) providing a sensor rigidly attached to the XY table and a handling arm supporting the block, said surface facing the XY table; b) for each of three non-aligned points of the surface of the block, displacing with respect to each other the XY table and the block in the X and/or Y directions to place the sensor opposite the point, and estimating, with the sensor, the distance along the Z direction between the point and the sensor; and c) modifying the orientation of the block by means of the handling arm to provide the desired parallelism.