Both the modern environmental monitoring and the home automation applications require new tailor made humidity sensor solutions. A significant group of humidity sensors is based on the property changes of porous thick and thin films [1]. Capacitive sensors make use of the dielectric property changes of such films upon water vapor uptake which depends on the surrounding media's relative humidity content [2]. However as the water molecules enter the porous layer beside the dielectric constant the thermal conductivity of the layer changes as well. Thermal transient testing, a well known technique for thermal characterization of IC packages [3] can be a suitable method for detecting humidity changes this way. In the paper this measuring technique is evaluated. Experiments were done on an appropriate sensor structure at different environments and relative humidity levels. Based on the results, a new method for humidity sensing is introduced. © EDA Publishing/THERMINIC 2008.