Recently a great interest has risen on the development of interfaces between molecular systems and traditional electronic or optoelectronic devices. Such devices can have a great number of applications, with the only limitation residing in the ability to obtain reproducible and controllable preparations. The use of a standard substrate, such as unoxidized crystalline silicon, offers many advantages, allowing the combination of the existing semiconductor production processes with the biological deposition. This is an extremely fertile field and has a number of promising applications such as genomics, proteomics, computational biology and pharmaceuticals. To develop this potential, we have developed a procedure to immobilize a DNA layer on a crystalline silicon substrate in order to exploit the high potentialities of crystalline silicon as substrate for DNA-based biodevices. Due to the requirements of a controlled preparation, we have thoroughly characterized every step of the preparation using different techniques. In this way we have also optimized the parameters in order to produce a high-quality proto-biosensor employable, in principle, in a number of applications.