An integrated optoelectronic silicon biosensor that can detect biomolecules by the change of the optical coupling between the integrated light source and the integrated detector that is caused by the binding of the appropriately labeled analytes onto the recognition molecules, that have been previously immobilized onto the integrated optical fiber that connects the optical source with the detector. The device contains the optoelectronic silicon chip and its biological activation. The optoelectronic chip is realized following integrated circuits fabrication methods so as the light source, the detector and the optical fiber, that optically couples the light source with the detector, to be monolithically integrated on the same silicon substrate. The biological activation of the chip is performed through physicochemical modification of the chip surface in order to permit immobilization of the recognition biomolecules onto the optical fiber surface. The biomolecules to be determined (proteins or oligonucleotides) are labeled with chromophore groups or nanoparticles or enzymes and after their coupling by the recognition biomolecules reduce the optical coupling between the light source and the detector providing a measure of their concentration.