A biosensor for triglycerides has been developed with porous silicon. Porous silicon was made from p-type crystalline silicon and it was thermally oxidized. Lipase enzyme was used to hydrolyze triglycerides, which results in the formation of acid. This causes a change in the pH of the solution. Here, the enzyme lipase was immobilized into the pores of the oxidized porous silicon via physical adsorption. Electrolyte-oxide-semiconductor (EOS) structure was realized with enzyme solution, oxidized porous silicon, porous silicon and crystalline silicon. The concentration of triglycerides in the electrolyte was determined by characterizing the above EOS structure for capacitance-voltage (C-V) measurements.