We have succeeded in developing a thermo-electric micro sensor designed with a three-dimensional electric wiring to measure the thermal diffusivity in micro scale. Temperature wave in the area of 12.5 mu m in diameter is observed as a periodical change of thermo electromotive force. The phase shift of temperature wave is measured by means of a lock-in method and the thermal diffusivity of polymer film is determined with a standard deviation less than 2%. The micro-scale distribution of thermal diffusivity in the banded structures of spherulites of poly-L-lactic acid (PLLA) is demonstrated. (C) 2011 Elsevier B.V. All rights reserved.