Using statistical design of experiments, the effect of ultrasonic pre‐treatment on the nucleation density of diamond was studied. The parameters investigated included ultrasonic excitation power, concentration of diamond powder in water, duration of ultrasonic excitation, and duration of cleaning with water after ultrasonic excitation. Diamond films were deposited on silicon (100) substrates using microwave assisted plasma chemical vapor deposition. The nucleation density varied from 106nuclei/cm2to 109nuclei/cm2. The results illustrated that the dominant effect in ultrasonic pre‐treatment was seeding. Moreover, scratches caused by the seeds during the treatment enabled more seeds to be retained on the surface. Based on these results, an optimized ultrasonic pretreatment has been developed. The new procedure yields a uniform nucleation density of 109nuclei/cm2on silicon (100) substrates. ©1995 American Institute of Physics.