The transport in miniaturised electronic devices requires to go beyond simple hydrodynamic descriptions. So, carrier transports in nano-length devices is no longer dominated by collisions among the particles but the ballistic transport governs at this level. This type of transport occurs when the perturbation characteristic time is of the order of the relaxation time and the mean free path is of the order of the device's dimension. The aim of the present work is to calculate the ballistic velocity of heat transport by using a continued-fraction technique in the framework of extended irreversible thermodynamics. This ballistic speed must be less or equal to the maximum value c0 corresponding to phonon speed. Note that the classical Fourier equation is only able to describe the diffusion regime and the Maxwell-Cattaneo equation predicts a second sound propagation at speed c0/Ö3 but it is silent about the ballistic behaviour .The transport in miniaturised electronic devices requires to go beyond simple hydrodynamic descriptions. So, carrier transports in nano-length devices is no longer dominated by collisions among the particles but the ballistic transport governs at this level. This type of transport occurs when the perturbation characteristic time is of the order of the relaxation time and the mean free path is of the order of the device's dimension. The aim of the present work is to calculate the ballistic velocity of heat transport by using a continued-fraction technique in the framework of extended irreversible thermodynamics. This ballistic speed must be less or equal to the maximum value c0 corresponding to phonon speed. Note that the classical Fourier equation is only able to describe the diffusion regime and the Maxwell-Cattaneo equation predicts a second sound propagation at speed c0/Ö3 but it is silent about the ballistic behaviour
