The aim of my PhD project is the development of versatile photonic sensors for labelfree detection of biomolecules on the basis of semiconductor microdisks. The detection principle bases on the shift of the frequency of optical whispering gallery modes. Each resonator will be functionalized by fixing molecules to its perimeter which can selectively bind to well defined partners as in the case for complementary DNA sequences or antigen/antibody combinations. The evanescent field of the optical mode polarizes a molecule attached to the resonator which in return shifts the mode frequency. For detection of the modal shift an add/drop filter scheme with integrated waveguides passing a series of microdisks at a small distance will be fabricated. Waveguides and microdisks can be etched simultaneously with standard semiconductor technologies from a single substrate to form an integrated device.