The bimaterial cantilever beam is an important basic structure of microelectromechanical system thermal devices. The research described in this paper is a study of the deflection of the bimaterial cantilever beam operated in the air and irradiated with a laser beam at the free end. The bimaterial cantilever beam is a composite structure formed by layers of silicon nitride and gold. The temperature variations produce the deflection of the cantilever beam end due to different values of the thermal expansion coefficients of silicon nitride and gold. The deflection was experimentally measured in vacuum and atmospheric pressure when a laser beam was irradiated at the free end. A formula for the calculation of the deflection as a function of incident power applied at the free end of the cantilever beam operated in air was also demonstrated. The predicted values of the deflection calculated using this formula and the experimental values of the deflection were compared, and the results were in good agreement. A systematic investigation of the cantilever beam deflection in vacuum and atmospheric pressure as a function of the heat applied at the free end is important for chemical and biological applications.