The paper reports the study of vibrations occurring in a thin silicon membrane of a conventional capacity pressure sensor. The 20 μ-thick silicon membrane has an area of 6×6 mm. Vibrations induced on the membrane with the help of electrical excitation were studied using a heterodyne laser probe. The probe output gives a measure of the amplitude of vibration of the membrane. Using this technique spatial response of the capacitive pressure sensor diaphragm has been carried out. The resonant frequency peaks of the membrane were measured and the effect of air pressure loading observed.