Abstract : novel biosensor based on a triangular resonator with a long evanescent field on a total internal reflection (TIR) mirror is proposed, and its sensing properties are analyzed for the first time. The sensing properties of the triangular ring resonator are found to be useful in realizing biological and chemical sensors, when the TIR mirror with a sharp incident angle increases the evanescent field owing to the Goos– Ha¨nchen shift. For transverse electric polarized light, an extinction ratio of 16 dB is achieved by changing the refractive index of 1  105 in the outer region of the TIR mirror block. Then, an extinction ratio of 28 dB and a resonance shift of 160pm are observed by changing the refractive index of 1  105 for transverse magnetic polarization.