The effect of substrate vibration at ultrasonic frequencies on thermoelectric properties (TEP) during the evaporation of CdS and CdSe films has been studied in detail. The temperature variation of the TEP has been explained. The carrier concentration n(c) and Fermi energy E-F of the films deposited on vibrating and nonvibrating substrates are compared. It is found that the effect of in situ substrate vibration during deposition is to decrease the extrinsic behaviour of the films by improving the stoichiometry.