The high thermoelectric properties were reported by using nano-structures for the reduction of thermal conductivity as well as keeping high electrical conductivity [1].Strong phonon scattering can be expected avoiding from the electron scattering in the structured semiconductors when the phonon mean free path is longer than the electron mean free path.In this study we intend to measure both electrical conductivity and thermal conductivity simultaneously using Si thin films with periodic micro-pores.The structured Si thin films were fabricated using silicon-on-insulator wafers by standard micro-fabrication processes.The both thermal and electrical conductivities measured by a self-heating method [2] were lower in the porous membranes than in the non-porous membrane.The measured thermal conductivity was much lower than the thermal conductivities expected by classical models [3].A significant phonon size effect was observed even in micro-sized structures,and the mean free path for phonons was very long.We concluded that phonon transport is quasi-ballistic and electron transport is diffuse in micro-porous Si structures.We also intend to make a thermal rectifier using the quasi-ballistic transport of phonons in an asymmetric structure.The thermal conductivity of Si thin films with triangle pores were measured,and the effects of the asymmetric structures on the phonon transport were discussed with numerical simulations of a phonon transport.