Microwave dielectric spectroscopy is a promising technique that allows intracellular, non-invasive, label-free and cost-effective biological studies. To complement the sensing possibilities of this technique at this frequency range, which have been previously demonstrated at the single cell, cellular suspensions and organs levels, a microwave-based sensor is designed, fabricated and evaluated to dielectrically characterize 3D biological microtissues. Such a biological model is indeed of high interest for biological investigations, as it constitutes an intermediate entity between 2D cell cultures and organs, exhibiting a biological response close to the one obtained with tissue physiology. The proposed sensor here the development of one of the first microfabricated device for spheroids studies. A discussion on the way of analyzing the data is proposed thanks the measurements of different fixed spheroids and polystyrene beads.