Laser based ultrasonic techniques provide a potential noninvasive sensing methodology to monitor the solid–liquid interface shape and position during crystal growth provided, the temperature dependence of the ultrasonic velocity for both solid and liquid phases are known a priori. A laser ultrasonic approach has been used to measure the ultrasonic velocity of single crystal solid and liquid Cd0.96Zn0.04Te as a function of temperature. The longitudinal wave velocity was found to be a strong monotonically decreasing function of temperature in the solid and liquid phases and exhibited an abrupt almost 50% decrease upon melting. Using both longitudinal and shear wave velocity values together with data for the temperature dependent density allowed a complete evaluation of the temperature dependent single crystal elastic stiffness constants (C11, C12, C44) for the solid and the adiabatic bulk modulus (KS) for the liquid. In addition, evaluation of the thermoelastic modulus (MT) has given insight on the impact of dislocation generation from excessive thermal gradient induced stresses during growth. The simplicity of making high temperature laser ultrasonic measurements together with the large longitudinal wave velocity difference between the solid and liquid phases suggests a laser based ultrasonic sensor has significant potential for sensing the solid–liquid interface during the growth of CdTe alloys. © 1998 American Institute of Physics.