Integrated polymeric waveguide biosensors are usually used for the detection of chemical/biological samples. To improve the sensitivity of the conventional waveguide sensors with only one sensing surface, we design and fabricate an improved sensing window with three sensing surfaces based on inductively coupled plasma etching method, whose sensitivity can be enhanced by a factor of 2.8 in theory. The effects of etching parameters, especially the antenna power, the bias power and the O-2 flow rate were systematically studied and the parameters were optimized to fabricate the sensing window. A single-mode balanced Mach-Zehnder interferometer waveguide biosensor with the improved sensing window was fabricated under this optimum etching condition, and presented a higher sensitivity than that of the sensor with conventional sensing window. This type of sensing window will be very useful in polymer waveguide biosensor devices. (C) 2012 Elsevier B.V. All rights reserved.