This paper describes, for the first time, the relative permittivity extraction of cells in their culture medium submitted to different stimuli by using a microwave biosensor, specifically developed to analyze single cells. The sensitive part of the device is constituted by a 5 μm coplanar gap, over which the cell is blocked by a mechanical trap. It allows to obtain the capacitive and conductive contrasts of a cell. Electromagnetic simulations where the cell (sphere) permittivity is tuned permit to define fitted calibration curves linking capacitive and conductive contrasts to the real and imaginary parts of the relative permittivity. Measurements are performed on various cells (in their culture medium) after different environmental stimuli in order to induce various biological stresses altering the cell state. Results show that this non-invasive technique, including the developed proper de-embedding post-process, provides the intrinsic dielectric image of single biological cells, which then reveals their biological state.