  We report on evaluation of lattice thermal conductivity of
GeTe/Sb$_{2}$Te$_{3}$ superlattice (SL) by using femtosecond coherent phonon
spectroscopy at various lattice temperatures. The time-resolved transient
reflectivity obtained in amorphous and crystalline GeTe/Sb$_{2}$Te$_{3}$ SL
films exhibits the coherent $A_{1}$ optical modes at terahertz (THz)
frequencies with picoseconds dephasing time. Based on the Debye theory, we
calculate the lattice thermal conductivity, including scattering by grain
boundary and point defect, umklapp process, and phonon resonant scattering. The
results indicate that the thermal conductivity in amorphous SL is less
temperature dependent, being attributed to dominant phonon-defect scattering.
