The aim of this work was the electrical characterization of biological molecules covalently immobilized on the dielectric of a MOS-like structure. The experimental protocol to bond the biological molecules on SiO2 lies in: oxide activation, silanization, linker molecule deposition, biological molecule bonding. Both an enzyme, the glucose oxidase (GOx), and single-stranded oligonucleotides (ssDNA) were selected as biological molecules. The effectiveness of the immobilization procedure was tested by X-ray Photoelectron spectroscopy. The electrical characterization was carried out on reference and fully processed samples as a function of the electrolyte pH, from 3 to 8, and of measurement time, up to 200 s. The oxide does not experience any aging during the measurement sets for voltages up to ±3 V. GOx deposition produces a shift of about −0.7 ± 0.04 V in the VFB, suggesting the molecule has a positive charge …