Silicon sensors can be fabricated as small, rugged and reliable chip devices with a broad field of applications in medicine, biotechnology, food analysis and environmental monitoring. Thus, there is an increasing demand in realizing such sensors for the determination of, e.g. chemical and biological quantities in aqueous solutions. By developing semiconductor-based field-effect structures, moreover, their main advantage is due to the combination of both the physical effect as the transducer principle and the deposition of the sensitive layers directly onto the silicon chip. In this work, different sensor types that are originated from the field effect are presented: The capacitive ElS (electrolyte-insulator-semiconductor) sensor is suitable for the pH detection using the capacitance/voltage technique. By immobilizing an additional enzyme layer, e.g. of penicillinase, a biosensor has been realized. Both sensors can be integrated as an EIS sensor array. The utilization of the porous silicon technology offers the possibility of a further miniaturization. The LAPS (light-addressable potentiometric sensor) is based on the identical ElS structure. Here, each measuring point on the surface can be arbitrarily addressed by a probing light. The resulting photocurrent is generated as the sensor signal. This arrangement also allows a two-dimensional mapping of the spatial distribution of ions or molecules.