An oscillator-based capacitive proximity sensor is presented. To improve the sensor's sensitivity by minimising the effect of parasitic capacitance, the proposed sensor employs a negative capacitance generation technique. The sensor is implemented with a standard 0.18''m CMOS technology, and the measurement results show that frequency variation is about 1.4' at 5'cm distance while only consuming an 85''A current. The die area occupies 520 by 280''m, and the size of an external sensing plate is 0.5 by 0.5'cm.