This paper presents results obtained with a biosensor whose operating mode is based on the association of two complementary parts, microfluidic channels and a RF circuit. The technological process of manufacturing the devices is entirely monolithic. A protocol for testing different fluids was conducted to validate the concept. The operating mode of these sensors is as follows: the RF parameters of the signal emitted by the electronic circuit will be modified by the presence of the liquid flowing in a network of channels buried in the substrate and positioned under RF patterns. So, the cutoff frequency of a stop-band microstrip stub can be modified and its variations could be related to the fluid nature and/or its components. Furthermore, these RF elements can be used as part of wireless communication circuits. For the first time in a bio-detection chip, resonators and micro-channels are integrated the ones under the others by a monolithic process; they are not reported or assembled in a hybrid device. Our practical approach consists to use a specific substrate, the photosensitive epoxy SU8 [K. Y. Lee, 1995], in order to associate channels network and metallic resonators circuits in the same integrated tridimensional chip. For this purpose, we have developed a specific technology to realize microfluidic structures by using lamination techniques [P. Abgrall, 2006]. Three configurations were realized and studied: channels empty, channels full with water, and channels full with a solution containing a biological entity, i.e. glutamine. The microsystems have been characterized with an RF signal whose the frequency varies between 10 GHz and 40 GHz. The results show a shift of respectively 24% and 3% of cut-off frequencies between the situation where the channel is filled with deionized water and glutamine solution at 0.2M compared to the empty channel. Hence, the operating cut-off frequency fluctuates between 19.1 GHz and 24.5GHz depending on the concentration of glutamine. These devices have been used also to detect and evaluate the concentration of NaCl in water. In the future, they will be used for other molecules or biologic entities like bacteria or virus.