AbstractAs a pressure sensor to be used at the tip of a catheter, a capacitive relative pressure sensor was fabricated. This paper describes the fabrication process and the characteristics of this pressure sensor.The size of the sensor fabricated is 0.7 × 3.5 × 0.8 mm3 and the spacing between the capacitor electrodes is either 1.0 μm or 1.5 μm. The principal features are as follows: (1) In the fabrication of the diaphragm, high‐concentration boron was diffused into an Si wafer. The diaphragm thickness was controlled accurately by etch stop; (2) to reduce the effect of the stray capacitance and to increase the S/N ratio of the sensor, the capacitance detection IC was placed near the diaphragm; (3) since the consumption current flows at the oscillation frequency, it is possible to use two lead wires from the sensor; and (4) this IC has a size of 1.2 × 0.5 mm2 and the temperature dependence of the oscillation frequency can be made zero by letting the power supply voltage be 2.24 V. The pressure sensitivity of the obtained sensor is 3.45 × 10−5/mmHg and the temperature coefficient at the zero pressure was 0.17 mmHg/°C. The output of the IC placed by the sensor had a frequency change of about 7 kHz for 1000 mmHg.