PURPOSE: To easily remove superfine particles of small grain sides by constituting an ultrasonic oscillator as a composite piezoelectric substance regularly arrayed with prismatic inorg. piezoelectric substances in a synthetic resin matrix and oscillating ultrasonic waves of a high frequency and high energy by the same.

CONSTITUTION: The ultrasonic oscillator 3 of the ultrasonic washing device constituted by mounting the ultrasonic oscillator 3 at the bottom of a washing tank 1 is constituted as the composite piezoelectric substance regularly arrayed with the prismatic inorg. piezoelectric substances 31 consisting of barium titanate or the like in the synthetic resin matrix 32, such as silicon, by which the ultrasonic waves of the high frequency and the high energy are oscillated. The synthetic resin of the matrix 32 has a modulus of elasticity of 1 to 50 kg.f/mm2 and the inorg. piezoelectric substance 31 has a moudlus of elasticity of 6,000 kg.f/mm2. Consequently, the superfine particles of the small grain sizes may be easily removed. Even the particles of intricate shapes may be washed and the easy washing of highly integrated semiconductor devices is made possible.