We examined the levels of serum α-fetoprotein, carcinoembryonic antigen, and carbohydrate antigen in 83 of 400 patients who had undergone surgery for gastric cancer and correlated these markers with stages of the disease. In addition, we measured C-reactive protein (CRP) concentrations in the sera of gastric cancer patients with silicon nanowire field-effect transistors (SiNW FETs) to determine whether SiNW FETs could be used to accurately sense CRP, a marker of inflammation and possible indicator of future progression of the cancer. We designed and fabricated SiNWs to be responsive to CRP. Of the 83 patients examined, six who showed marked elevation of CRP (>3 to 10 mg/dL, according to hospital laboratory measurements) were selected and subjected to measurement with the SiNW FETs. Our findings showed that SiNW-based sensors could be highly sensitive and specific in measuring CRP in the sera of postoperative patients and thus could represent a simple and quick method of prognostic evaluation in patients. From the Clinical Editor In this study, silicon nanowire field effect transistors were fabricated to be responsive to C-reactive protein. The new technology resulted in highly sensitive and specific CRP sensors, which may greatly simplify this serum test for a variety of conditions where rapid, accurate and easily repeatable CRP measurements are needed.