This paper presents a gauge pressure sensor based on the standard industrial flexible PCB (FPCB) technology. The wireless LC-resonant sensor consists of a variable sensing capacitor and a planar inductor coil fabricated in FPCB. The air gap of the sensing capacitor is extended through a pressure channel embedded in the FPCB strip to enable relative pressure measurement. Thus, the intracranial pressure (ICP) with respect to local atmosphere can be measured without other calibration means. The flat FPCB structure also facilitates the subdural implantation procedures. Experimental results showed that the proposed gauge pressure sensors with such open sensing structures had much higher frequency sensitivity (0.29%/mmHg) compared with sensors with sealed sensing cavities (0.005%/mmHg) and achieved a resolution of 0.51 mmHg.