Recently, circulating microRNAs (miRNAs) in body fluids have been reported as one of the cancer diagnostic biomarkers, and detection of miRNAs is expected to improve early cancer diagnosis. In this study, a surface-functionalized power-free (SF-PF) microchip for miRNA detection was fabricated by applying UV-light-induced graft polymerization of poly(2-aminoethyl methacrylate) to a poly(dimethylsiloxane) power-free microchip and by immobilizing capture probe DNA to the graft chains. The required time, sample volume, and limit of detection of miR-500a-3p were 18 min, 0.5 mu L, and 41 fmol/L, respectively. In addition, the SF-PF microchip could be stored at ambient temperature and humidity for at least 1 week.