To implement a semiconductor laser diode for use in high density optical data storage systems, the output laser beam must be first collimated and then focussed to a near diffraction-limited spot. Therefore, it is essential to know both the beam intensity profile and the phase distribution of the laser wavefront with high precision on the order of one fiftieth of a wavelength. This measurement is important to both the laser diode manufacturers and users. In this paper, we will describe how the wavefront of a laser diode collimator pen was measured by using a state-of-the-art phase measurement interferometer built by WYKO Optical, Inc. Performance of this interferometer is evaluated using both He-Ne and diode lasers.