Thermal diffusivity of thin film with low dielectric constant (k), what is called low-k dielectric thin film, 0.31-1.14 mu m, including hydrogen-silsesquioxane (HSQ), methyl-silsesquioxane (MSQ), and poly(arylen ether) was examined by temperature wave analysis. The phase shift of temperature wave was observable up to 100 kHz. Thermal diffusivity of HSQ was 47 x 10(7) m(2) s(-1), on the other hand it was not higher than 1.1 x 10(-7) m(2) s(-1) for MSQ or poly(arylen ether) at room temperature. Temperature dependence of thermal diffusivity/thermal conductivity of MSQ was obtained, thermal diffusivity decreased but thermal conductivity increased in a heating scan at 30-150 degrees C. It was shown that the thermal diffusivity of low-k thin film was correlated with the chemical and the physical structures, the latter was formed in the spin-coating and the curing process. (c) 2005 Elsevier B.V. All rights reserved.