This paper is concerned with the well‐posedness and asymptotic behaviour of solutions to a laminated beam in thermoelasticity of type III. We first obtain the well‐posedness of the system by using semigroup method. We then investigate the asymptotic behaviour of the system through the perturbed energy method. We prove that the energy of system decays exponentially in the case of equal wave speeds and decays polynomially in the case of nonequal wave speeds. Under the case of nonequal wave speeds, we also investigate the lack of exponential stability of the system.