The chemical imaging sensor is a semiconductor-based chemical sensor that can visualize the two-dimensional distribution of chemical species in the specimen. One of the prospective applications of the chemical imaging sensor is the visualization of biochemical activities in biological systems. The chemical imaging sensor was successfully applied for the detection of Escherichia coli colonies. For further applications to biological systems, enhanced adhesion of the sample to the sensing surface seems to be indispensable. As a candidate material for biocompatible sensors, porous Si was tested and was found to have a high PH sensitivity of 57.3 mV/pH.